Changes definitions for VAX SQL.

Additional information available:

DATABASESTORAGE_MAPDOMAININDEXSCHEMATABLE

 ALTER DATABASE -+-> PATHNAME path-name -+--+
                 +-> FILENAME file-spec -+  |
 +---------------<--------------------------+
 ++------------->--------------+------------+
  +-> alter-root-file-params1 -+            |
 +------------------------------------------+
 ++-------------->-------------+------------+
  +-> alter-root-file-params2 -+            |
 +------------------------------------------+
 ++-------------->----------------+---------+
  +-> alter-storage-area-params --+         |
 +---------------<--------------------------+
 +++--------------------------->------------------++>;
  |+-> ADD STORAGE AREA area-name ----------+     ||
  ||+---------------------------------------+     ||
  ||++----------->---------+> storage-area-params-+|
  || +> FILENAME file-spec +                      ||
  |+> ALTER STORAGE AREA area-name --------+      ||
  ||+--------------------------------------+      ||
  ||+> alter-storage-area-params -----------------+|
  |+> DROP STORAGE AREA area-name ----------------+|
  +-----------------------------<------------------+

Additional information available:

ADD_STORAGE_AREAALTER_STORAGE_AREADROP_STORAGE_AREA

More Informationalter root file params1alter root file params2alter storage area params
storage area params

 Alters a database in any of the following ways:

  o  For both single-file and multifile databases, changes
     characteristics of the database root file associated with a
     database.  ALTER DATABASE allows you to override certain
     characteristics specified in the root file parameters of a CREATE
     DATABASE statement, such as whether the snapshot file is
     disabled.  In addition, ALTER DATABASE lets you control other
     characteristics that you cannot specify in CREATE DATABASE root
     file parameters, such as whether after-image journaling is
     enabled.

  o  For both single-file and multifile databases, changes storage
     area parameters.

  o  For multifile databases only, adds, alters, or drops storage
     areas.

 Specifies the name and file specification for a storage area you want
 to add to the database.  You can use the ADD STORAGE AREA clause only
 on multifile databases.  The storage area name cannot be the same as
 any other storage area name in the database.

 The ADD STORAGE AREA clause creates two files, a storage area file
 with a file type of .RDA and a snapshot file with a file extension of
 .SNP.  If you omit the FILENAME argument, the file specification
 takes the following defaults:

  o  Device:  the current device for the process

  o  Directory:  the current directory for the process

  o  File name:  the name specified for the storage area


 The file specification is used for both the data and snapshot files
 that comprise the storage area (unless you use the SNAPSHOT FILENAME
 argument to specify a different file for the snapshot file).  Because
 the ADD STORAGE AREA clause may create two files with different file
 types, do not specify a file type with the file specification.

 If you use the ALTER DATABASE statement to add a storage area, the
 change will not be journaled.  You should, therefore, back up your
 database before making such a change.  See the Usage Notes for
 important information about changes that are not journaled.

 Specifies the name of an existing storage area in the database that
 you want to alter.  You can use the ALTER STORAGE AREA clause only on
 multifile databases.

 SQL generates an error if you specify RDB$SYSTEM as the storage area
 name in the ALTER STORAGE AREA clause.  If you want to change the
 parameters of the RDB$SYSTEM storage area using the ALTER DATABASE
 statement, you must specify the storage area parameters outside of
 the ALTER STORAGE AREA clause.

 alter-root-file-params1 =

  +-+-+-> MULTISCHEMA IS -----+--> ON ---+----------+-+-+>
  | | |                       +--> OFF --+          | | |
  | | +-> OPEN IS ------------+--> AUTOMATIC  -+----+ | |
  | | |                       +--> MANUAL -----+    | | |
  | | +-> READ WRITE -------------------------------+ | |
  | | +-> NUMBER OF USERS IS --> number-users ------+ | |
  | | +-> NUMBER OF BUFFERS IS --> number-buffers --+ | |
  | | +-> NUMBER OF VAXCLUSTER NODES IS ----------+ | | |
  | | |    +--------------------------------------+ | | |
  | | |    +-> number-nodes ------------------------+ | |
  | | +-> NUMBER OF RECOVERY BUFFERS IS ----------+ | | |
  | | |    +--------------------------------------+ | | |
  | | |    +-> number-buffers ----------------------+ | |
  | | +-> SNAPSHOT IS -+> ENABLED -+------->-----+-++ | |
  | | |                |           +> IMMEDIATE -+ |  | |
  | | |                |           +> DEFERRED --+ |  | |
  | | |                +> DISABLED ----------------+  | |
  | | +-> global-buffers-params ----------------------+ |
  | +----------------------------<--------------------+ |
  +-----> READ ONLY ------------->----------------------+

Additional information available:

READ_ONLYREAD_WRITE

More Informationglobal buffer params

 Parameters that control the characteristics of the database root file
 associated with the database, or characteristics stored in the root
 file that apply to the entire database.  You can specify these
 parameters for either single-file or multifile databases.

 Note that ALTER DATABASE does not allow you to change all root file
 parameters you can specify in CREATE DATABASE.  You must use the
 EXPORT and IMPORT statements to change the following root file
 parameters:

  o  BUFFER SIZE

  o  NUMBER OF USERS (for a single-file database)

  o  NUMBER OF VAXCLUSTER NODES (for a single-file database)

  o  SEGMENTED STRING STORAGE AREA

  o  PROTECTION IS ANSI

  o  PROTECTION IS ACL

 global-buffer-params=

  -> GLOBAL BUFFERS ARE -+-> ENABLED --+---+
                         +-> DISABLED -+   |
  +----------------------------------------+
  +-+-----------------------------------------------+->
    +-> ( -> NUMBER IS number-glo-buffers -> , --+  |
         +---------------------------------------+  |
         +-> USER LIMIT IS max-glo-buffers ----> ) -+

 Use the READ ONLY option to change a read/write RDB$SYSTEM storage
 area (and the Rdb/VMS system relations stored in the area) to
 read-only.  You might choose the READ ONLY option if your database is
 never or rarely updated.  When the RDB$SYSTEM storage area is changed
 to read-only, locking conflicts occur less frequently, and the
 automatic updating of index and relation cardinality is inhibited.

 For information on changing a read/write storage area other than the
 RDB$SYSTEM storage area to read-only, see the "READ_ONLY" subtopic
 for "alter_storage_area_params".

 Use the READ WRITE option to change a read-only RDB$SYSTEM storage
 area (and the Rdb/VMS system relations stored in the area) to
 read/write.

 For information on changing a read-only storage area other than the
 RDB$SYSTEM storage area to read/write, see the "READ_WRITE" subtopic
 for "alter_storage_area_params".

 alter-root-file-params2 =
 -+-+-> DICTIONARY IS ------+-> REQUIRED -------+---------+-+>
  | |                       +-> NOT REQUIRED ---+         | |
  | +-> ADJUSTABLE LOCK GRANULARITY IS -+-+-> ENABLED ----+ |
  | +-> CARRY OVER LOCKS ARE -----------+ +-> DISABLED ---+ |
  | +-> LOCK TIMEOUT INTERVAL IS number-seconds SECONDS --+ |
  | +-> JOURNAL FILENAME file-spec -----------------------+ |
  | +-> JOURNAL ALLOCATION IS -> journal-blocks -> BLOCKS + |
  | +-> JOURNAL EXTENT IS ---> extent-blocks --> BLOCKS --+ |
  | +-> NO JOURNAL ---------------------------------------+ |
  | +-> journal-fast-commit-clause -----------------------+ |
  +---------------------------------------------------------+

Additional information available:

More Informationjournal fast commit clause

 Parameters that control the characteristics of the database root file
 associated with the database, or characteristics stored in the root
 file that apply to the entire database.  You can specify these
 parameters for either single-file or multifile databases.

 DICTIONARY IS REQUIRED specifies that definition statements issued
 for the database must also stored in the data dictionary.

 ADJUSTABLE LOCK GRANULARITY Enables or disables whether or not the
 database system will automatically maintain as few locks as possible
 on database resources.  The default is ENABLED, and results in fewer
 locks against the database.

 JOURNAL FILENAME specifies the file for the database system to use as
 the after-image journal (.AIJ) file.  By default, when you create a
 database, after-image journaling is disabled.  Specifying an .AIJ
 file in the ALTER DATABASE statement enables after-image journaling.

 JOURNAL ALLOCATION IS specifies the number of blocks allocated for
 the .AIJ file.  The default is 0 blocks.

 JOURNAL EXTENT IS specifies the number of blocks of each .AIJ file
 extent.  The default extent for .AIJ files is 512 blocks.

 NOJOURNAL discontinues after-image journaling for databases that
 previously had it enabled.

 journal-fast-commit-clause =

 -> JOURNAL FAST COMMIT --+-> ENABLED --+-----+
                          +-> DISABLED -+     |
  +-------------------------------------------+
  ++-----------------------------------------------+>
   +>(++-> CHECKPOINT INTERVAL IS n BLOCKS ----++>)+
      |+-> CHECKPOINT TIMED EVERY n SECONDS ---+|
      |+-> COMMIT TO JOURNAL OPTIMIZATION -----+|
      |+-> NO COMMIT TO JOURNAL OPTIMIZATION --+|
      |+-> TRANSACTION INTERVAL IS number-txns +|
      +-------------------- , <-----------------+

Additional information available:

More InformationExample

 JOURNAL FAST COMMIT ENABLED specifies that Rdb/VMS keeps updated
 pages in the buffer pool and does not write the pages to disk each
 time a transaction commits.

 The updated pages can remain in the buffer pool until a
 user-specified threshold (called a checkpoint) is reached.  At
 checkpoint, Rdb/VMS writes all the updated pages for multiple
 transactions to disk.  If a transaction fails, Rdb/VMS rolls back the
 current, failed transaction and reprocesses all the committed
 transactions since the last checkpoint.

 Fast commit processing applies only to erase, modify, and store
 operations.  Transactions that include data definition statements,
 such as create logical area or create index operations, force a
 checkpoint at the end of the transaction.

 You can specify a checkpoint after a certain number of blocks using
 the CHECKPOINT INTERVAL IS clause or after a time period using the
 CHECKPOINT TIMED EVERY clause.  If you specify both types of
 checkpoints, Rdb/VMS checkpoints at whichever one it reaches first.

 If you enable COMMIT TO JOURNAL OPTIMIZATION when you enable fast
 commit, Rdb/VMS does not write commit information to the database
 root file.  This option enhances performance in database environments
 that are update intensive.  Because of the prerequisites for enabling
 the journal optimization option, general use databases or databases
 that have many read-only transactions may not benefit from this
 feature.  For more information see the VAX Rdb/VMS Guide to Database
 Maintenance and Performance.

 The TRANSACTION INTERVAL IS n clause specifies the size of the TSN
 range where n equals the number of TSNs (transaction sequence
 numbers).  Rdb/VMS uses transaction sequence numbers to ensure
 database integrity.  When you specify NO COMMIT TO JOURNAL
 OPTIMIZATION, TSNs are assigned to users one at a time.  When the
 journal optimization option is enabled, each user is pre-assigned a
 range of TSNs.  Assigning a range of TSNs avoids the single-threading
 problem because commit information need not be written to the
 database root for each transaction.  Rdb/VMS writes all transaction
 information to the .AIJ file except for each user's allocated TSN
 range, which it writes to the root.

 The transaction interval value (the TSN range) must be a number
 between 8 and 1024.  The default value is 256.  You need to decide
 which constraint has precedence on your database:  performance or
 running out of TSNs.

 As a general guideline, if your database has few users or if all user
 sessions are long, select a high transaction interval.  If your
 database has many users or if user sessions are short, select a
 smaller transaction interval.

 The following example changes the CORPORATE_DATA database so that
 after-image journaling and fast commit processing are enabled.

 SQL> ALTER DATABASE FILENAME CORPORATE_DATA
 cont> JOURNAL FILENAME DISK01:[DEPT3.SQL]CORP_DATA.AIJ
 cont> JOURNAL FAST COMMIT ENABLED
 cont> (CHECKPOINT INTERVAL IS 100 BLOCKS,
 cont> CHECKPOINT TIMED EVERY 10 SECONDS);
 %RDMS-I-AIJMODSEQ, next AIJ file sequence number will be 2
 SQL>

 alter-storage-area-params =

 -+-+-+---> READ WRITE --------------------------------------++->
  | | +-+-> EXTENT IS +-> ENABLED ----+---------------------++|
  | | | |             +-> DISABLED ---+                     |||
  | | | |             +-> extent-pages ---------> PAGES --+-+||
  | | | |             +-> (extension-options) ------------+ |||
  | | | +-------------------------<-------------------------+||
  | | +---> SNAPSHOT ALLOCATION IS -> snp-pages --> PAGES ---+|
  | | +---> SNAPSHOT EXTENT IS -+> extent-pages -> PAGES -+--+|
  | |                           +> (extension-options) ---+  ||
  | +-------------------------------<------------------------+|
  +-------> READ ONLY ----------------------------------------+
  +-------> WRITE ONCE ---------------------------------------+

Additional information available:

EXTENTEXTENT_ISREAD_ONLYREAD_WRITE
SNAPSHOT_ALLOCATION_ISSNAPSHOT_EXTENT_ISWRITE_ONCE

More Informationextension options

 Parameters that change the characteristics of database storage area
 files.  You can specify the same storage area parameters for either
 single-file or multifile databases, but the effect of the clauses in
 this part of an ALTER DATABASE statement differs:

  o  For single-file databases, the storage area parameters change the
     characteristics for the single storage area in the database.

  o  For multifile databases, the storage area parameters change the
     characteristics of the RDB$SYSTEM storage area.  SQL generates an
     error if you specify RDB$SYSTEM as the storage area in the ALTER
     STORAGE AREA clause, so specifying the parameters in this part of
     the ALTER DATABASE statement is the only way to change the
     parameters of the RDB$SYSTEM storage area using the ALTER
     DATABASE statement.


 Note that the ALTER DATABASE statement does not allow you to change
 all storage area parameters you can specify in the CREATE DATABASE
 statement.  You must use the EXPORT and IMPORT statements to change
 the following database root file parameters:

  o  ALLOCATION

  o  PAGE SIZE

  o  PAGE FORMAT

  o  THRESHOLDS

  o  INTERVAL

  o  SNAPSHOT FILENAME

 Enables or disables extents.  Extents are ENABLED by default, and can
 be changed online, but the new extents are not immediately effective
 on all nodes of a cluster.  On the node on which you have changed
 extents, the new storage area extents are immediately effective for
 all users.  The new storage area extents become effective as the
 database is attached on each node of the cluster.

 Disabling extents helps diagnose performance problems caused by
 faulty area sizing when creating hashed with mixed page format.

 Changes the number of pages of each storage area file extent.  See
 the description under the "SNAPSHOT EXTENT" argument.

 Permits you to change any read/write storage area (except the
 RDB$SYSTEM storage area) to read-only.

 For information on changing a read/write RDB$SYSTEM storage area to
 read-only, see the "READ_ONLY" subtopic for
 "alter_root_file_params1".

Additional information available:

More Information

 SQL provides support for both read-only databases and databases with
 one or more read-only storage areas.  You can take advantage of this
 read-only support if you have a stable body of data that is never (or
 rarely) updated.

 Read-only databases consist of:

  o  A read/write root file

  o  One or more read-only storage areas and no read/write storage
     areas


 Read-only databases can be published and distributed on CDROM media.

 Read-only storage areas:

  o  Have snapshot files, but do not use them.  (Data in a read-only
     storage area is not updated; specify a small number for the
     initial snapshot file size for a read-only storage area.)

  o  Eliminate page and record locking in the read-only storage areas.

  o  Are backed up by the RMU/BACKUP command by default unless you
     explicitly state /NOREAD_ONLY which excludes read-only areas
     without naming them.

  o  Are restored by the RMU/RESTORE command if they were previously
     backed up.

  o  Are recovered by the RMU/RECOVER command.  However, unless the
     read-only attribute was modified, the read- only area does not
     change.

  o  Are not recovered by the RMU/RECOVER/AREA=* command, where you
     are not explicitly naming the areas needing recovery, unless they
     are inconsistent.


 If you change a read/write storage area to read-only, you cannot
 specify the EXTENT, SNAPSHOT ALLOCATION, and SNAPSHOT EXTENT clauses.

 A database with both read/write and read-only storage areas can be
 fully recovered after a system failure ONLY if after-image journaling
 is enabled on the database.  If your database has both read/write and
 read-only storage areas but does not have after-image journaling
 enabled, you should do full backups (including read-only areas) at
 all times.  Doing full backups enables you to recover the entire
 database to its condition at the time of the previous backup.

 Permits you to change any read-only storage area (except the
 RDB$SYSTEM storage area) to read/write.  You might change a read-only
 storage area to read/write to facilitate batch updates to
 infrequently changed data.

 For information on changing a read-only RDB$SYSTEM storage area to
 read/write, see the "READ_WRITE" subtopic for
 "alter_root_file_params1".

 Changes the number of pages allocated for the snapshot file.  The
 default is 100 pages.  If you have disabled the snapshot file, you
 can set the snapshot allocation to 0 pages.

 Changes the number of pages of each snapshot or storage area file
 extent.  The default extent for storage area files is 100 pages.

 Specify a number of pages for simple control over the file extent.
 For greater control, and particularly for multivolume databases, use
 the MINIMUM, MAXIMUM, and PERCENT GROWTH extension options instead.

 If you use the MINIMUM, MAXIMUM, and PERCENT GROWTH parameters, you
 must enclose them in parentheses.

 Permits you to change any storage area that contains only a segmented
 string to a format that can be stored on a write-once, read-many
 (WORM) device.

 You can use the WRITE ONCE option to change a storage area containing
 stable database list (segmented string) data to a format that can be
 stored on a write-once, read-many (WORM) optical disk.  A WORM
 optical disk offers a relatively inexpensive way of storing large
 amounts of data for read-only access compared to other storage media.
 Rdb/VMS supports the Perceptics WORM optical disk drive and juke box
 as a storage media for storing lists or segmented string data.
 Example 2 at the end of this section shows how to change a read/write
 storage area to a write-once storage area.
 5More_Information
 The following restrictions apply to the WRITE ONCE option:

  o  You cannot write data other than segmented strings to a
     write-once storage area.  Rdb/VMS issues an error message if you
     try to create a storage map that stores data other than segmented
     strings in a write-once storage area.  Storage maps for
     non-segmented-string data must be removed before you can alter a
     storage area to WRITE ONCE.

  o  When you create a storage area on WORM media, you must specify
     that the snapshot area remains on read/write media; do not give a
     snapshot file the WRITE ONCE attribute.

  o  If you specify the WRITE ONCE option when storing a segmented
     string, database keys are not compressed.

  o  Although write-once storage areas do not use SPAM pages to look
     for storage space, but to assist moving data back to non-WORM
     media in which SPAM pages must be built again, space is still
     allocated for them.  Because SPAM pages are essential in uniform
     areas, write-once storage areas can of uniform format and
     therefore are required to be of mixed format.

  o  You can use the PAGE SIZE IS clause of CREATE STORAGE AREA to
     change the default page size for a storage area.  To optimize
     storage, always specify an even number of blocks per page.

  o  Digital does not support magnetic media for storing write-once
     storage areas.

  o  After you move a storage area to or from a WORM device, Digital
     recommends that you back up your database completely and start a
     new after-image journaling file.

 extention-options =

 ---> MINIMUM OF min-pages PAGES, ---+
 +-----------------------------------+
 +--> MAXIMUM OF max-pages PAGES, ---+
 +-----------------------------------+
 +--> PERCENT GROWTH IS growth --------->

 Changes the number of pages of each snapshot or storage area file
 extent.

Additional information available:

MINIMUM_OFMAXIMUM_OFPERCENT_GROWTH_IS

 Specifies the minimum number of pages of each extent.  The default is
 100 pages.

 Specifies the maximum number of pages of each extent.  The default is
 10,000 pages.

 Specifies the percent growth of each extent.  The default is 20
 percent growth.

 Deletes the specified storage area definition and the associated data
 and snapshot files.  You can use the DROP STORAGE AREA clause only on
 multifile databases.

 To protect against accidental data deletion, the ALTER DATABASE
 statement fails if you specify a DROP STORAGE AREA clause that names
 a storage area referred to in any storage map.  You must first use
 the ALTER STORAGE MAP statement to move the data to another storage
 area.

 storage-area-params =

 -++-------------------------->-----------------------------++->
  |+-> ALLOCATION IS ---> number-pages ----> PAGES ---------+|
  |+-> PAGE SIZE IS ----> page-blocks -----> BLOCKS --------+|
  |+-> PAGE FORMAT IS --+----> UNIFORM ----+----------------+|
  ||                    +----> MIXED ------+                ||
  |+-> THRESHOLDS ARE ( val1 -+----------------------+-> ) -+|
  ||                          +-> ,val2 -+----------++      ||
  ||                                     +-> ,val3 -+       ||
  |+-> INTERVAL IS -------> number-data-pages --------------+|
  |++> EXTENT IS ----+--> ENABLED ---------------------+-+--+|
  |||                +--> DISABLED --------------------+ |  ||
  |||                +--> extent-pages ----> PAGES ----+ |  ||
  |||                +--> (extension-options) ---------+ |  ||
  ||+----------------------------<-----------------------+  ||
  |+-> SNAPSHOT FILENAME ---> file-spec --------------------+|
  |+-> SNAPSHOT ALLOCATION IS --> snp-pages --> PAGES ------+|
  |+-> SNAPSHOT EXTENT IS -+-> extent-pages --> PAGES -+----+|
  ||                       +-> (extension-options) ----+    ||
  |+-> WRITE ONCE ------------------------------------------+|
  +-----------------------------<----------------------------+

 Parameters that control the characteristics of the storage area.

 ALTER STORAGE MAP map-name -+
 +---------------------------+
 +--+-+-> store-clause ---------------------+-+--+-->;
    | +-> threshold-clause -----------------+ |  |
    | ++-> ENABLE --+-> COMPRESSION --------+ |  |
    | |+-> DISABLE -+                       | |  |
    | +-> NO PLACEMENT VIA INDEX -----------+ |  |
    | +-> PLACEMENT VIA INDEX index-name ---+ |  |
    | +-> REORGANIZE --> --+---->------+------+  |
    |                      +-> AREAS --+         |
    |                      +-> PAGES --+         |
    +--------------------<-----------------------+

Additional information available:

More Informationstore clausethreshold clausestore lists clause

 Changes an existing storage map.  A storage map controls which rows
 of a table are stored in which storage areas in a multifile database.

 In addition to changing storage maps, ALTER STORAGE MAP has options
 that change:

  o  Which index the database system uses when inserting rows in the
     table

  o  Whether the rows of the table will be stored in a compressed
     format

  o  Whether the data in the existing storage areas will be
     reorganized

  o  Which columns of the table will be stored in an area

 store clause =

 -> STORE ---+----------------------------------------+-->
             +-> IN area-name ---------------------+  |
             |  +----------------------------------+  |
             |  ++----------------------------------+-+
             |   +-> ( --> threshold-clause --> )---+ |
             +-> across-clause -----------------------+
             +-> using-clause ------------------------+

Additional information available:

More Information

 A new storage map definition that replaces the existing storage map.
 The store clause allows you to specify which storage area files will
 be used to store rows from the table:

  o  All rows of a table can be associated with a single storage area.

  o  Rows of a table can be distributed among several storage areas.

  o  Rows of a table can be systematically distributed, or
     partitioned, among several storage areas by specifying upper
     limits on the values for a column in a particular storage area.
     This is called horizontal partitioning.

 threshold-clause =

  -+-> THRESHOLD -+-> IS -+-> ( --> val1 --> ) -----+->
   |              +-> OF -+                         |
   |                                                |
   +-> THRESHOLDS -+-> ARE -+-----------+           |
                   +-> OF  -+           |           |
     +----------------------------------+           |
     +-> ( --> val1 -+-----------------------+-> ) -+
                     +-> , val2 -+-----------+
                                 +-> , val3 -+

Additional information available:

More Information

 You can specify up to three SPAM thresholds for storage areas with
 mixed format pages and logical areas in storage areas with uniform
 format pages.  The value val represents the percentage of the
 partition.

 You can specify a default threshold for a new logical area using the
 THRESHOLDS ARE clause in the ALTER STORAGE MAP statement.  To specify
 thresholds for a particular storage area, each storage area mentioned
 in the STORE clause can be followed by a THRESHOLDS ARE clause.

 Thresholds are not allowed for segmented string storage areas.  The
 THRESHOLD clause only applies to new areas:  you cannot change a
 threshold for a logical area.

 Although a threshold clause associated with a particular area is
 enclosed in parentheses, the default threshold clause for a storage
 map is not.  (The threshold clause associated with a particular area
 appears within the store clause.)

 store-lists-clause =

 --->  STORE LISTS ---+
   +------------------+
   +-+->  IN -+-> area-name ----------+--------+---------->
     |        +-> (-+> area-name + ) -+        |
     |              +---- , <----+             |
     | +---------------------------------------+
     | +-+------------------------------------------------->-+
     |   +-> FOR -> ( -+-> table-name -----------+-> ) -+    |
     |                 +-> table-name. col-name -+      |    |
     |                 +-------- , <-------------+      |    |
     |           +--------------------------------------+    |
     |           +---+-----------------------+------------->-+
     |               +-> FILL RANDOMLY  -----+               |
     |               +-> FILL SEQUENTIALLY --+               |
     +----<--------------------------------------<-----------+

Additional information available:

FOR

More InformationExample

 Directs the database system to store the lists from tables in a
 specified storage area or in a set of areas.  You can create only one
 storage map for lists within each database.

 You must specify a default storage area for lists in the STORE LISTS
 clause.  The default list storage area contains lists from system
 tables as well as lists not directed elsewhere by the STORE LISTS
 clause.  You can also use the LIST STORAGE AREA clause of the CREATE
 DATABASE statement to specify a default storage area for lists.  If
 you do not use the STORE LISTS clause and do not specify a list
 storage area in the CREATE DATABASE statement, Rdb/VMS uses
 RDB$SYSTEM as the default list storage area.

  o  (table-name)

     Specifies the table or tables to which this storage map will
     apply.  If you want to store lists of more than one table in the
     storage area, separate the names of the tables with commas.  For
     each area, you can specify one FOR clause and list of
     table-names.

  o  (table-name.col-name)

     Specifies the name of the table and column containing the list to
     which this storage map will apply.  Separate the table name and
     the column name with a period (.).  If you want to store multiple
     lists in the storage area, separate the table name-column name
     combinations with commas.  For each area, you can specify one FOR
     clause and list of column names.  You cannot specify the same
     table and column name more than once in the same storage map.

Additional information available:

FILL RANDOMLY and FILL SEQUENTIALLY

 Specifies whether to fill the area set randomly or sequentially.
 Specifying FILL RANDOMLY or FILL SEQUENTIALLY requires a FOR clause.
 When a storage area is filled, it is removed from the list of
 available areas.  Rdb/VMS does not attempt to store any more lists in
 that area during the current database attach.  Instead, Rdb/VMS
 starts filling the next specified area.

 When a set of areas is filled sequentially, Rdb/VMS stores lists in
 the first specified area until that area is filled.  Use sequential
 filling when storing lists in write- once storage areas in a jukebox
 environment to avoid excess swapping of platters.  In a jukebox
 environment, the filled storage area is marked with a FULL flag and
 the platter on which the area resides is no longer swapped in.

 If the set of areas is filled randomly, lists are stored across
 multiple areas.  This is the default.  Random filling is intended for
 read/write media which will benefit from the I/O distribution across
 the storage areas.

 The keywords FILL RANDOMLY and FILL SEQUENTIALLY can only be applied
 to areas contained within an area list.

 The following example causes list data to be stored in several
 storage areas.  You cannot control which records are stored in which
 storage areas, nor can you use ALTER STORAGE MAP to move list data to
 another storage area.

 SQL> ALTER STORAGE MAP LISTS_MAP
 cont> STORE LISTS IN RDB$SYSTEM
 cont> FOR (RESUMES.RESUME)
 cont> IN RESUME_LISTS
 cont> FOR (RESUMES.RESUME)
 cont> IN RESUME_LISTS2
 cont> FOR (RESUMES.RESUME);
 SQL> SHOW STORAGE MAP LISTS_MAP
      LISTS_MAP
  For Lists
  Store clause:          STORE LISTS IN RDB$SYSTEM
      FOR (RESUMES.RESUME)
      IN RESUME_LISTS
      FOR (RESUMES.RESUME)
      IN RESUME_LISTS2
      FOR (RESUMES.RESUME)

 The following example creates a new column for an existing table, and
 alters the storage map to specify a storage area for that column.

 SQL> ALTER TABLE RESUMES ADD PICTURE LIST OF VARBYTE.
 SQL> ALTER STORAGE MAP LISTS_MAP
 cont> STORE LISTS IN RESUME_LISTS FOR (RESUMES.RESUME)
 cont> IN RESUME_LISTS2
 cont> FOR (RESUMES.PICTURE);

 ALTER DOMAIN ----+
  +---------------+
  +->domain-name +-----------------+-+-----------------++
                 +-> IS data-type -+ +->default-value -+|
  +-----------------------------------------------------+
  +-+--------------------------------------------+--+
    +---> COLLATING SEQUENCE IS sequence-name ---+  |
    +---> NO COLLATING SEQUENCE -----------------+  |
          +-----------------------------------------+
          +--+--------------------------+--> ;
             ++-> sql-and-dtr-clause --++
              +-------<----------------+

Additional information available:

COLLATING_SEQUENCE_ISNO_COLLATING_SEQUENCE

More Informationdomain namedata typedefault valuesql and dtr clause

 Alters a domain definition.  This allows you to change the character
 set, data type, optional default value, optional collating sequence,
 or optional formatting and DATATRIEVE clauses associated with a
 domain name.  Any table definitions that refer to that domain reflect
 the changes.

 For example, if you want to change the data type for EMPLOYEE_ID from
 CHAR(5) to CHAR(6), you need only alter the data type for ID_DOM.
 You do not have to alter the data type for the column EMPLOYEE_ID in
 the tables DEGREES, EMPLOYEES, JOB_HISTORY, SALARY_HISTORY, nor do
 you have to alter the column MANAGER_ID in DEPARTMENTS.

 You can alter any named domain once you have attached to the database
 that includes the domain.  If you want to alter a domain that is
 referred to in an index definition, you must first drop the index.

 You can change the character set associated with a domain name.
 However, if this is done after data is entered into a table using the
 domain name, SQL returns a data conversion error when you try to
 select rows from that table.

 If a domain definition is stored in the data dictionary, the ALTER
 DOMAIN statement alters the domain definition in the data dictionary.

 The name of a domain you want to alter.  The domain name must be
 unique among domain names in the schema.

 data-type =
  -+-> char-data-types ---------------------------+-->
   +-> TINYINT --------------+-----+--------+-----+
   +-> SMALLINT -------------+     +-> (n) -+     |
   +-> INTEGER --------------+                    |
   +-> BIGINT ---------------+                    |
   +-> LIST OF BYTE VARYING -+                    |
   +-> DECIMAL -+-+-----------------------------+-+
   +-> NUMERIC -+ +-> ( --> n -+--------+-> ) --+ |
   |                           +-> , n -+         |
   +-> FLOAT -+--------+--------------------------+
   |          +-> (n) -+                          |
   +-> REAL --------------------------------------+
   +-> DOUBLE PRECISION --------------------------+
   +-> date-time-data-types ----------------------+

Additional information available:

char data types

 char-data-types =

 -+-> CHAR  +--------+-+-------------------------------------+-+->
  |         +-> (n) -+ +-> CHARACTER SET character-set-name -+ |
  +-> NCHAR ---------+-+--------+------------------------------+
  +-> NATIONAL CHAR -+ +-> (n) -+                              |
  +-> VARCHAR (n) -----+-------------------------------------+-+
  |                    +-> CHARACTER SET character-set-name -+ |
  +-> NCHAR VARYING ----------+------+---------+---------------+
  +-> NATIONAL CHAR VARYING --+      +-> (n) --+               |
  +-> LONG VARCHAR  -------------------------------------------+

Additional information available:

CHARVARCHAR

character set nameNCHAR or NATIONAL CHARNCHAR VARYING or NATIONAL CHAR VARYING

 The CHAR data type can be qualified by the keywords CHARACTER SET and
 the character set name.

 A valid character set for database object names.

 The NCHAR or NATIONAL CHAR data type has the same characteristics as
 CHAR, except that the character set is that specified as the national
 character set.

 The NCHAR VARYING or NATIONAL CHAR VARYING data type has the same
 characteristics as VARCHAR, except that the character set is that
 specified as the national character set.

 The VARCHAR data type can be qualified by the keywords CHARACTER SET
 and the character set name.

 This data type has the same characteristics as CHAR, except that the
 character set is that specified in the CHARACTER SET clause.

 default-value =

 DEFAULT --+-->literal -----------+->
           +-->USER  -------------+
           +-->NULL  -------------+
           +-->CURRENT_DATE  -----+
           +-->CURRENT_TIME  -----+
           +-->CURRENT_TIMESTAMP -+

Additional information available:

USERNULLCURRENT_DATECURRENT_TIMECURRENT_TIMESTAMP

literalMore Information

 A value expression that is either numeric, character string, or date.

 The user name of the process that invokes interactive SQL or runs a
 program.

 A null value.

 DATE data type value containing year, month, and day for date
 'today'.

 TIME data type value containing hour, minute, and second for time
 'now'.

 TIMESTAMP data type value containing year, month, and day for date
 'today' and hour, minute, and second for time 'now' currently defined
 in Rdb/VMS.

 The default value of a column is the value stored in the database if
 an insert operation on a row specifies no value for that column.  You
 can use literals, the NULL keyword, the current timestamp, or the
 user name as default values.  If you do not specify a default value,
 SQL assigns NULL as the default value.

 If you specify a default value for a column in a table, it overrides
 any default value specified for the domain on which the column is
 based.

 You might have any of several possible reasons for specifying a
 default value for a column; for instance, you may want to store the
 most commonly used value, or you may want to store a value that
 highlights (visually displays) the fact that no value was stored.

 Specifies a new collating sequence for the named domain.

 The VMS National Character Set (NCS) Utility provides a set of
 pre-defined collating sequences and also lets you define collating
 sequences of your own.  The COLLATING SEQUENCE clause accepts both
 pre-defined and user-defined NCS collating sequences.

 Before you use the COLLATING SEQUENCE clause in an ALTER DOMAIN
 statement, you must first specify the NCS collating sequence for SQL
 using the CREATE COLLATING SEQUENCE statement.  The sequence-name
 argument in the COLLATING SEQUENCE clause must be the same as the
 sequence-name in the CREATE COLLATING SEQUENCE statement

 Specifies that the named domain will use the standard default
 collating sequence:  that is, ASCII.  Use the NO COLLATING SEQUENCE
 clause to override the collating sequence defined for the database in
 the CREATE DATABASE or ALTER DATABASE statement, or the domain in the
 CREATE DOMAIN statement.

 sql-and-dtr-clause =

 -+-> QUERY HEADER IS -+> quoted-string --+-----------------+->
  |                    +------ / <--------+                 |
  +-> EDIT STRING IS quoted-string -------------------------+
  |                                                         |
  +-> QUERY NAME FOR -+-> DTR --------+-> IS quoted-string -+
  |                   +-> DATATRIEVE -+                     |
  +-> DEFAULT VALUE FOR -+-> DTR --------+-> IS literal ----+
                         +-> DATATRIEVE -+





 Optional formatting clauses allow you to modify data displays or
 query characteristics for interactive SQL users and DATATRIEVE users.

 A query header specifies a string that interactive SQL or DATATRIEVE
 displays in place of the column name when it retrieves values from a
 column.  An edit string specifies a string that controls how
 interactive SQL or DATATRIEVE formats the display of values in a
 column.

 DEFAULT VALUE and QUERY NAME are active only from DATATRIEVE.

 ALTER INDEX index-name -+
                         |
  +----------------------+
  ++-------------------------------------+-+
   +-+-+-> NODE SIZE number-bytes ---+-+-+ |
     | +-> PERCENT FILL percentage --+ |   |
     | +-> USAGE --+-> UPDATE ---+---+ |   |
     |             +-> QUERY ----+     |   |
     +---------- <---------------------+   |
                                           |
  +----------------------------------------+
  ++-------------------------+---------------> ;
   +-> index-store-clause ---+

Additional information available:

More Informationindex store clause

 Changes an index.  The ALTER INDEX statement allows you to change:

  o  The characteristics of index nodes (sorted indexes only)

  o  The names of the storage area or storage areas that contain the
     index

  o  Thresholds for the logical storage areas that will contain the
     index


 You cannot change:

  o  The columns that comprise an index

  o  Whether the index is UNIQUE

  o  A hashed index to a sorted index

  o  A sorted index to a hashed index


 You cannot alter an index when there are other active users of the
 database.

 index-store-clause = STORE -+
 +---------------------------+
 ++-> IN area-name ---+--------------------------------+-+->
  |                   +-> ( -> threshold-clause -> ) --+ |
  |                                                      |
  +-> USING -> ( -+-> column-name -+-> ) -------------+  |
                  +--------<-------+                  |  |
  +---------------------------------------------------+  |
  ++> IN area-name -+-------------------------------+-+  |
   |                +-> ( -> threshold-clause -> ) -+ |  |
   | +------------------------------------------------+  |
   | +-> WITH LIMIT OF -> ( -+-> literal -+-> ) ------+-+|
   |                         +------<-----+           | ||
   +---------------------<----------------------------+ ||
                                                        ||
 +------------------------------------------------------+|
 +--> OTHERWISE IN area-name -----+                      |
     +----------------------------+                      |
     +-+----------------------------------+--------------+
       +-> ( --> threshold-clause ---> ) -+

Additional information available:

threshold clauseMore Information

 threshold-clause =

  -+-> THRESHOLD -+-> IS -+-> ( --> val1 --> ) -----+->
   |              +-> OF -+                         |
   |                                                |
   +-> THRESHOLDS -+-> ARE -+-----------+           |
                   +-> OF  -+           |           |
     +----------------------------------+           |
     +-> ( --> val1 -+-----------------------+-> ) -+
                     +-> , val2 -+-----------+
                                 +-> , val3 -+

 A storage map definition for the index.  You can specify a store
 clause for indexes in a multifile database only.  The STORE clause in
 a CREATE INDEX statement allows you to specify which storage area
 files will be used to store the index entries:

  o  All index entries can be associated with a single storage area.

  o  Index entries can be systematically distributed, or partitioned,
     among several storage areas by specifying upper limits on the
     values for a key in a particular storage area.

  o  You can specify a different SPAM threshold for each logical area
     that is created by a storage map.  You can specify a default
     threshold for any new logical area using the THRESHOLDS ARE
     clause in the ALTER INDEX statement.

     To specify thresholds for a particular storage area, each storage
     area mentioned in the STORE clause can be followed by a
     THRESHOLDS ARE clause.  The value val represents the percentage
     of the partition.

 If you omit the storage map definition, the default is to store all
 the entries for an index in the main RDB$SYSTEM storage area.

 The ALTER SCHEMA statement is supported only for upward
 compatibility.  For information on altering databases see the Help
 topic on ALTER DATABASE.

 ALTER TABLE --> table-name --+
 +----------------------------+
 +-+-+-> ADD -+-> COLUMN col-definition ---------+--> ;
   | |        +-> CONSTRAINT table-constraint ---+
   | +-> ALTER alter-col-definition -------------+
   | +-> DROP -+-> COLUMN column-name -----------+
   |           +-> CONSTRAINT constraint-name ---+
   +---------------------<-----------------------+

Additional information available:

ADD_COLUMNADD_CONSTRAINTDROP_COLUMNDROP_CONSTRAINT

More Informationtable namealter col definition

 The ALTER TABLE statement changes an existing table definition.  You
 can:

  o  Add columns

  o  Add constraints to tables or columns

  o  Modify columns

  o  Modify character sets

  o  Modify data types

  o  Delete columns

  o  Delete constraints

 The name of the table whose definition you want to change.

 The ADD COLUMN clause creates an additional column in the table.  SQL
 adds the column to the right of the existing columns in the table.

 col-definition =

  -> column-name ----+
     +---------------+
     +-+-> data-type ---+-+------------------+-+
     | +-> domain-name -+ +-> default-value -+ |
     | +---------------------------------------+
     | ++-------------------+-+-----------------------+-+->
     |  ++> col-constraint ++ +-> sql-and-dtr-clause -+ |
     |   +--------<--------+                            |
     +--> COMPUTED BY value-expr -----------------------+

 Specify a name for the column, a data type or domain name, and
 optional default value, column-constraints, and SQL and DATATRIEVE
 formatting clauses for the column specified by the column name.

Additional information available:

COMPUTED_BY

data typedomain namedefault valuecol constraintsql and dtr clause

 data-type =
  -+-> char-data-types ---------------------------+-->
   +-> TINYINT --------------+-----+--------+-----+
   +-> SMALLINT -------------+     +-> (n) -+     |
   +-> INTEGER --------------+                    |
   +-> BIGINT ---------------+                    |
   +-> LIST OF BYTE VARYING -+                    |
   +-> DECIMAL -+-+-----------------------------+-+
   +-> NUMERIC -+ +-> ( --> n -+--------+-> ) --+ |
   |                           +-> , n -+         |
   +-> FLOAT -+--------+--------------------------+
   |          +-> (n) -+                          |
   +-> REAL --------------------------------------+
   +-> DOUBLE PRECISION --------------------------+
   +-> date-time-data-types ----------------------+

Additional information available:

More-Informationchar data types

 A valid SQL data type.  Specifying an explicit data type to associate
 with a column is an alternative to specifying a domain name.

 Using the ALTER clause to change the data type of a column (directly
 or indirectly by specifying a domain) requires caution:

  o  If you change a column to a data type with a larger capacity, or
     increase the scale factor for a column, you may have to modify
     source programs that refer to the column and precompile them
     again.

  o  If you change a column to a data type with a smaller capacity,
     SQL truncates values already stored in the database that exceed
     the capacity of the new data type, but only when it retrieves
     those values.  (The values are not truncated in the database,
     however, until they are updated.  If you only retrieve data,
     therefore, you can change the data type back to the original, and
     SQL again retrieves the entire original value.)

  o  You can change a DATE column only to a character data type (CHAR,
     VARCHAR, LONG VARCHAR, NCHAR, NATIONAL CHAR, NCHAR VARYING, or
     NATIONAL CHAR VARYING).  If you attempt to change a DATE column
     to anything but a character data type, you could get unexpected
     results.

 char-data-types =

 -+-> CHAR  +--------+-+-------------------------------------+-+->
  |         +-> (n) -+ +-> CHARACTER SET character-set-name -+ |
  +-> NCHAR ---------+-+--------+------------------------------+
  +-> NATIONAL CHAR -+ +-> (n) -+                              |
  +-> VARCHAR (n) -----+-------------------------------------+-+
  |                    +-> CHARACTER SET character-set-name -+ |
  +-> NCHAR VARYING ----------+------+---------+---------------+
  +-> NATIONAL CHAR VARYING --+      +-> (n) --+               |
  +-> LONG VARCHAR  -------------------------------------------+

 A charcter-set-name is a valid character set for database object
 names.

 The name of a domain created in a CREATE DOMAIN statement.  SQL gives
 the column the data type specified in the domain.

 default-value =

 DEFAULT --+-->literal -----------+->
           +-->USER  -------------+
           +-->NULL  -------------+
           +-->CURRENT_DATE  -----+
           +-->CURRENT_TIME  -----+
           +-->CURRENT_TIMESTAMP -+

Additional information available:

USERNULLCURRENT_DATECURRENT_TIMECURRENT_TIMESTAMP

More Informationliteral

 The default value of a column is the value stored in the database if
 an insert operation on a row specifies no value for that column.  You
 can use literals, the NULL keyword, the current timestamp, or the
 user name as default values.  If you do not specify a default value,
 SQL assigns NULL as the default value.

 If you specify a default value for a column in a table, it overrides
 any default value specified for the domain on which the column is
 based.

 You might have any of several possible reasons for specifying a
 default value for a column; for instance, you may want to store the
 most commonly used value, or you may want to store a value that
 highlights (visually displays) the fact that no value was stored.

 A value expression that is either numeric, character string, or date.

 The user name of the process that invokes interactive SQL or runs a
 program.

 A null value.

 DATE data type value containing year, month, and day for date
 'today'.

 TIME data type value containing hour, minute, and second for time
 'now'.

 TIMESTAMP data type value containing year, month, and day for date
 'today' and hour, minute, and second for time 'now' currently defined
 in Rdb/VMS.

 col-constraint=
  ---+----------------->------------+---+
     +->CONSTRAINT constraint-name -+   |
   +------------------------------------+
   +-> PRIMARY KEY -----------------+
   +-> UNIQUE ----------------------+
   +-> NOT NULL --------------------+
   +-> CHECK (predicate) -----------+
   +-> references-clause -----------+
   +------------>-------------------+
   +-------------<------------------+
   +----+----------------------------+-->
        +--> constraint-attributes --+

Additional information available:

constraint nameMore Informationreferences clauseconstraint attributes

 The optional CONSTRAINT constraint-name specifies a name for a column
 constraint that is used in several ways:

  o  The INTEG_FAIL error message specifies the name when an INSERT,
     UDPATE, or DELETE statement violates the constraint

  o  ALTER TABLE DROP CONSTRAINT statements specify the name to drop a
     table constraint

  o  SHOW TABLE statements display the names of column and table
     constraints


 The name of the constraint is used in error messages and ALTER TABLE
 DROP CONSTRAINT, SHOW TABLE, DECLARE TRANSACTION and SET TRANSACTION
 statements.  The CONSTRAINT clause is optional.  If you omit the
 constraint name, SQL creates a name.  However, DIGITAL recommends
 that you always name column and table constraints.  The constraint
 names generated by SQL may be obscure and, in programs, may change
 between compilation and running.

 A col-constraint is a constraint definition that applies to the
 specified column.  The five types of column constraints are PRIMARY
 KEY, NOT NULL, UNIQUE, CHECK, and foreign key constraints.  Foreign
 key constraints are created with the REFERENCES clause.  You can also
 optionally specify a name for a constraint definition.

 The PRIMARY KEY column constraint declares a column to be a primary
 key.  SQL requires that values in this column be unique and not null.
 Therefore, you need not specify the UNIQUE and NOT NULL column
 constraints for a primary key column.

 The NOT NULL column constraint restricts values in the column to
 non-null values.

 The UNIQUE column constraint specifies that values in the column
 named must be unique.  You can use either UNIQUE or PRIMARY KEY
 keywords to define a column as a unique key for a table.

 The CHECK column constraint specifies a predicate that column values
 inserted into the table must satisfy.  Predicates in CHECK table
 constraints can refer directly only to the column with which they are
 associated.

 references-clause =

 REFERENCES referenced-table-name ---+
  +-----------------<----------------+
  +-+--------------------->-------------------+->
    +-> ( -+-> referenced-column-name -+-> ) -+
           +----------- , <------------+

 Specifies the name of a column or columns that are a unique key or
 primary key in the referenced table.  When the REFERENCES clause is
 selected as a column-constraint, the column specified in the
 col-definition clause becomes a foreign key for the referencing table
 (the table being defined).  When the REFERENCES clause is selected as
 a table constraint, the column name or column names specified in the
 FOREIGN KEY clause become a foreign key for the referencing table.

 The referenced_table_name is the name of the table that contains the
 unique key or primary key referenced by the referencing table.  You
 must have the SQL access right REFERENCES or CREATETAB to the
 referenced table to declare a constraint that refers to another
 table..

 For a column constraint, the referenced_column_name is the name of
 the column that is a unique key or primary key in the referenced
 table.  For a table constraint, the the referenced_column_name is the
 name of the column or columns that are a unique key or primary key in
 the referenced table.  The unique key can be defined with either the
 UNIQUE or PRIMARY KEY keywords.  If you omit the
 referenced_column_name, the primary key is selected by default.

 constraint-attributes =

 ----+----> --+- DEFERRABLE -------->
     +-> NOT -+

 There are two constraint-attributes:

 Specifying NOT DEFERRABLE means that evaluation of the constraint
 must take place when the INSERT, DELETE, or UPDATE statement
 executes.

 Specifying DEFERRABLE means that evaluation of the constraint can
 take place at any later time.  Unless otherwise specified, evaluation
 of the constraint will take place as the COMMIT statement executes.
 You can use the SET ALL CONSTRAINTS statement to have all constraints
 evaluated earlier.  See the SET ALL CONSTRAINTS statement for more
 information.

 If you are using the default SQLV40 dialect, the default
 constraint-attribute is DEFERRABLE.  When using this dialect, Rdb/VMS
 displays a deprecated feature message for all constraints defined
 without specification of one of the constraint attributes.  The
 default constraint-attribute may change in a future release.  If you
 are using the SQL92 dialect, the default is NOT DEFERRABLE.

 sql-and-dtr-clause =

 -+-> QUERY HEADER IS -+> quoted-string --+-----------------+->
  |                    +------ / <--------+                 |
  +-> EDIT STRING IS quoted-string -------------------------+
  |                                                         |
  +-> QUERY NAME FOR -+-> DTR --------+-> IS quoted-string -+
  |                   +-> DATATRIEVE -+                     |
  +-> DEFAULT VALUE FOR -+-> DTR --------+-> IS literal ----+
                         +-> DATATRIEVE -+





 Optional formatting clauses allow you to modify data displays or
 query characteristics for interactive SQL users and DATATRIEVE users.

 A query header specifies a string that interactive SQL or DATATRIEVE
 displays in place of the column name when it retrieves values from a
 column.  An edit string specifies a string that controls how
 interactive SQL or DATATRIEVE formats the display of values in a
 column.

 DEFAULT VALUE and QUERY NAME are active only from DATATRIEVE.

 The COMPUTED BY clause specifies that the value of this column is
 calculated from values in other columns and constant expressions.
 You can use the ALTER TABLE COMPUTED BY clause to add a computed
 column to an existing table, but you cannot use it to alter an
 existing column into a computed column.
 In a COMPUTED BY clause, the column name that you supply in your
 column definition must be different from the name of any other
 existing column in the table.
 Any column that you refer to in the definition of a computed column
 cannot be deleted from that table unless you first delete the
 computed column.
 SQL does not allow UNIQUE or PRIMARY KEY constraints, REFERENCE
 clauses, default values, or default values for DATATRIEVE in computed
 columns.

 The ADD CONSTRAINT clause adds a table constraint definition that
 applies to the whole table.  The four types of table constraints are
 PRIMARY KEY, UNIQUE, CHECK, and FOREIGN KEY constraints.  You can
 also optionally specify a constraint name.

Additional information available:

table constraint

 table-constraint =
 ---+---------------->------------------+----+
    +-> CONSTRAINT constraint-name -----+    |
  +------------------------------------------+
  +-> PRIMARY KEY -> ( -+-> column-name -+-> ) ------+
  |                     +------- , <-----+           |
  +-> UNIQUE -> ( -+-> column-name -+-> ) -----------+
  |                +------- , <-----+                |
  +-> CHECK (predicate) -----------------------------+
  +-> FOREIGN KEY -> ( -+-> column-name -+-> ) --+   |
                        +------- , <-----+       |   |
    +-----------------------<--------------------+   |
    +-> references-clause ------------->-------------+
    +------------------------------------------------+
    +-----+---------------------------+------------->
          +-> constraint-attributes --+

Additional information available:

More Informationreferences clauseconstraint attributes

 The CONSTRAINT clause specifies a name for the table-constraint.  The
 name is used for a variety of purposes:

  o  The INTEG_FAIL error message specifies the name when an INSERT,
     UDPATE, or DELETE statement violates the constraint

  o  The ALTER TABLE DROP CONSTRAINT statements specify the constraint
     name

  o  The SHOW TABLE statements display the names of constraints

  o  The EVALUATING clause of SET and DECLARE TRANSACTION statements
     specifies constraint names


 The PRIMARY KEY constraint is used to declare a column or columns as
 a primary key for the table being altered.  Any foreign key that
 refers to this column must refer to this primary key.

 The UNIQUE table constraint specifies the name of a column or columns
 in the table being defined that are part of a unique key.

 The CHECK table constraint specifies a predicate that column values
 inserted into the table must satisfy.  Predicates in CHECK column
 constraints can refer directly only to the column with which they are
 associated.  Predicates in CHECK table constraints can refer to any
 column in the table.  Column select expressions within the predicate
 can refer to other tables in the schema.

 The FOREIGN KEY table constraint specifies the column or columns that
 you want to declare as a foreign key in the table you are altering
 (the referencing table).

 references-clause =

 REFERENCES referenced-table-name ---+
  +-----------------<----------------+
  +-+--------------------->-------------------+->
    +-> ( -+-> referenced-column-name -+-> ) -+
           +----------- , <------------+

 Specifies the name of a column or columns that are a unique key or
 primary key in the referenced table.  When the REFERENCES clause is
 selected as a table constraint, the column name or column names
 specified in the FOREIGN KEY clause become a foreign key for the
 referencing table.

 constraint-attributes =

 ----+----> --+- DEFERRABLE -------->
     +-> NOT -+

 There are two constraint-attributes:

 Specifying NOT DEFERRABLE means that evaluation of the constraint
 must take place when the INSERT, DELETE, or UPDATE statement
 executes.

 Specifying DEFERRABLE means that evaluation of the constraint can
 take place at any later time.  Unless otherwise specified, evaluation
 of the constraint will take place as the COMMIT statement executes.
 You can use the SET ALL CONSTRAINTS statement to have all constraints
 evaluated earlier.  See the SET ALL CONSTRAINTS statement for more
 information.

 If you are using the default SQLV40 dialect, the default
 constraint-attribute is DEFERRABLE.  When using this dialect, Rdb/VMS
 displays a deprecated feature message for all constraints defined
 without specification of one of the constraint attributes.  The
 default constraint-attribute may change in a future release.  If you
 are using the SQL92 dialect, the default is NOT DEFERRABLE.

 The ALTER COLUMN clause modifies the column specified by the column
 name:

 alter-col-definition =

 -> column-name -+-------->-------+-+--------->--------+--+
                 +-> data-type ---+ +-> default-value -+  |
                 +-> domain-name -+                       |
   +------------------------------------------------------+
   +---+------------>------------+---+
       ++> add-col-constraint --++   |
        +-----------<-----------+    |
   +---------------------------------+
   +--+------------>--------------------+--->
      +-+-> sql-and-dtr-clause ------+--+
        +--------------<-------------+

Additional information available:

More Informationdata typedomain namedefault valueadd col constraint
sql and dtr clause

 You can modify some elements of a column definition, but not others:

  o  You cannot change the column name.

  o  You can change an explicitly specified data type to another, but
     use care (see notes in this argument description).

  o  You can add or modify the default value.

  o  You can change the domain referred to by a column, provided the
     domain exists in the database

  o  You can substitute an explicit data type for a column that
     previously referred to a domain name

  o  If you do not want to change the data type or domain of an
     existing column, you do not need to specify a data type or domain
     name.

  o  You cannot change an existing column constraint.  However, you
     can delete the existing constraint and add a new column
     constraint using the alter-col-definition clause to achieve the
     same result.

  o  You can specify any column to be NOT NULL.  The only way you can
     alter an existing constraint to be not null is by using the ALTER
     TABLE statement.

  o  You can change a formatting clause by redefining clauses or
     overriding existing clauses with NO options.  If you add a new
     clause, existing clauses are unaffected.

 data-type =
  -+-> char-data-types ---------------------------+-->
   +-> TINYINT --------------+-----+--------+-----+
   +-> SMALLINT -------------+     +-> (n) -+     |
   +-> INTEGER --------------+                    |
   +-> BIGINT ---------------+                    |
   +-> LIST OF BYTE VARYING -+                    |
   +-> DECIMAL -+-+-----------------------------+-+
   +-> NUMERIC -+ +-> ( --> n -+--------+-> ) --+ |
   |                           +-> , n -+         |
   +-> FLOAT -+--------+--------------------------+
   |          +-> (n) -+                          |
   +-> REAL --------------------------------------+
   +-> DOUBLE PRECISION --------------------------+
   +-> date-time-data-types ----------------------+

Additional information available:

char data types

 char-data-types =

 -+-> CHAR  +--------+-+-------------------------------------+-+->
  |         +-> (n) -+ +-> CHARACTER SET character-set-name -+ |
  +-> NCHAR ---------+-+--------+------------------------------+
  +-> NATIONAL CHAR -+ +-> (n) -+                              |
  +-> VARCHAR (n) -----+-------------------------------------+-+
  |                    +-> CHARACTER SET character-set-name -+ |
  +-> NCHAR VARYING ----------+------+---------+---------------+
  +-> NATIONAL CHAR VARYING --+      +-> (n) --+               |
  +-> LONG VARCHAR  -------------------------------------------+

 A charcter-set-name is a valid character set for database object
 names.

 The name of a domain created in a CREATE DOMAIN statement.  SQL gives
 the column the data type specified in the domain.

 default-value =

 DEFAULT --+-->literal -----------+->
           +-->USER  -------------+
           +-->NULL  -------------+
           +-->CURRENT_DATE  -----+
           +-->CURRENT_TIME  -----+
           +-->CURRENT_TIMESTAMP -+

Additional information available:

USERNULLCURRENT_DATECURRENT_TIMECURRENT_TIMESTAMP

More Informationliteral

 The default value of a column is the value stored in the database if
 an insert operation on a row specifies no value for that column.  You
 can use literals, the NULL keyword, the current timestamp, or the
 user name as default values.  If you do not specify a default value,
 SQL assigns NULL as the default value.

 If you specify a default value for a column in a table, it overrides
 any default value specified for the domain on which the column is
 based.

 You might have any of several possible reasons for specifying a
 default value for a column; for instance, you may want to store the
 most commonly used value, or you may want to store a value that
 highlights (visually displays) the fact that no value was stored.

 A value expression that is either numeric, character string, or date.

 The user name of the process that invokes interactive SQL or runs a
 program.

 A null value.

 DATE data type value containing year, month, and day for date
 'today'.

 TIME data type value containing hour, minute, and second for time
 'now'.

 TIMESTAMP data type value containing year, month, and day for date
 'today' and hour, minute, and second for time 'now' currently defined
 in Rdb/VMS.

 The add-col-constraint clause specifies a constraint definition that
 applies to an existing column.  The syntax and explanation for the
 add-col-constraint clause are the same as for the col-constraint
 clause.

 sql-and-dtr-clause =

 -+-> QUERY HEADER IS -+> quoted-string --+-----------------+->
  |                    +------ / <--------+                 |
  +-> EDIT STRING IS quoted-string -------------------------+
  |                                                         |
  +-> QUERY NAME FOR -+-> DTR --------+-> IS quoted-string -+
  |                   +-> DATATRIEVE -+                     |
  +-> DEFAULT VALUE FOR -+-> DTR --------+-> IS literal ----+
                         +-> DATATRIEVE -+





 Optional formatting clauses allow you to modify data displays or
 query characteristics for interactive SQL users and DATATRIEVE users.

 A query header specifies a string that interactive SQL or DATATRIEVE
 displays in place of the column name when it retrieves values from a
 column.  An edit string specifies a string that controls how
 interactive SQL or DATATRIEVE formats the display of values in a
 column.

 DEFAULT VALUE and QUERY NAME are active only from DATATRIEVE.

 The DROP COLUMN statement deletes the specified column.

 The DROP CONSTRAINT statement deletes the specified column constraint
 or table constraint from the table definition.