Creates an index for a relation.  An index allows Rdb/VMS direct
 access to the records in the relation, to avoid sequential searching.
 You can define a sorted index or a hashed index.  A sorted index uses
 the B-tree method of retrieval.  A hashed index uses hash addressing
 for exact match retrievals.

 Example

   RDO>  DEFINE INDEX EMP_EMPLOYEE_ID FOR EMPLOYEES
   cont>   DUPLICATES ARE NOT ALLOWED
   cont>   TYPE IS SORTED.
   cont>     EMPLOYEE_ID.
   cont>  END EMP_EMPLOYEE_ID INDEX.

Additional information available:

MoreFormatExamples

 To define an index for a relation using the DEFINE INDEX statement,
 you need the Rdb/VMS DEFINE privilege for the relation.

 When the DEFINE INDEX statement executes, Rdb/VMS adds the index
 definition to the physical database.  If you have invoked the
 database with the PATHNAME specification, the definition is also
 added to the data dictionary.

 If you define a sorted index for a relation that contain no data, the
 root node for the index is not created until the first record is
 stored.  When an RMU/VERIFY operation encounters a sorted index with
 no root node, it reports the index as empty.

 You must execute this statement in a read/write transaction.  If you
 issue this statement when there is no active transaction, Rdb/VMS
 starts a read/write transaction implicitly.

 You cannot define a hashed index in a single-file database.

 If you define a hashed index, you must specify a storage map for it
 with the index-store-clause.  The storage area that you specify must
 have a MIXED page format.

 An optional keyword that causes Rdb/VMS to create ascending or
 descending index segments.  If you omit the ASCENDING or DESCENDING
 keywords, ASCENDING is the default.  To sort records in a particular
 way in the result of a particular query, specify the sort order in
 the SORTED BY clause.

 Other users are allowed to be attached to the database when you issue
 the DEFINE INDEX statement.

 DEFINEINDEX name ───┬────────────────>──────────────┬─────────┐
                      └─> 
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 ┌─────────────────────────────<────────────────────────────────┘
 └> Ftypebox (O)typebox (R) relation-name ┬─────────>──────────┬┬──────────>───────────┬─┐
                      └> duplicates-clause ┘└> index-store-clause ─┘ │
 ┌────────────────────────────────<──────────────────────────────────┘
 └─┬─────────────>───────────────┬───────────────────────────┬──┐
   ├─> 
T
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   └──────────────> sorted-index-param-list ─────────────────┘  │
 ┌───────────────────────── . <─────────────────────────────────┘
 └┬─> field-name ──┬─┬───────>────────────────┬─┬──┬────┐
  │                │ ├> 
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  │                │ ├> 
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  │                │ │> 
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  │                │ └> 
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  │                └────────────<───────────────┘  │    │
  └───────────────────────── . <───────────────────┘    │
 ┌──────────────────────────<───────────────────────────┘
 └─> 
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         └─> name ┘

Additional information available:

TYPE_ISASCENDINGDESCENDINGSIZE_ISMAPPING_VALUES

nametextrelation-namefield-nameduplicates-clause
index-store-clausesorted-index-param

 The name of the index.  You can use this name to refer to the index
 in other statements.  When choosing a name, follow these rules:

  o  Use a name that is unique among all index names in the database.

  o  Use any valid VMS name.  However, the name cannot end in a dollar
     sign ($) or underscore (_).

  o  Do not use any Rdb/VMS reserved words (see The VAX Rdb/VMS
     Reference Manual appendix for reserved words).

 A text string that adds a comment to the index definition.

 The name of the relation that includes the index.

 The name of the field(s) that make up the index.  You can create a
 multisegment index by naming two or more fields, which are joined to
 form the index.  All of the fields must be part of the same relation.
 Separate multiple field names with periods.

                                 NOTE

         If field-name refers to a field defined as VARYING
         STRING data type, the size of the field must be less
         than or equal to 255.

 duplicates-clause =

 ───> 
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                       └─> 
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 A clause specifying whether each value of the index must be unique.
 If you try to store the same value twice in an indexed field defined
 as DUPLICATES NOT ALLOWED, Rdb/VMS returns an error message and does
 not store or modify the record.

 index-store-clause

 STORE ─┬──> 
W
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H
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N ────> storage-area-name ─────────────>─────────┬─>
 ┌──────┘                                                          │
 │                                                                 │
 └─────> 
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G ───┬────> field-name ───┬── 
W
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H
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N ───────>─────┐   │
                  └────────── , ───────┘                       │   │
 ┌───────────────────────────────<─────────────────────────────┘   │
 └─┬─> storage-area-name ──> 
W
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   │                                        └──── , <───┘     │ │  │
   └───────────────────────────<──────────────────────────────┘ │  │
 ┌─────────────────────────────<────────────────────────────────┘  │
 │                                                                 │
 └─────────────────────> storage-area-name ───────────>────────────┘

 The index-store-clause creates a storage map definition for the
 index.  It allows you to choose which storage area files will be used
 to store index entries.  You can store all index entries for one
 relation in a single storage area, or you can partition the entries
 over multiple storage areas.

Additional information available:

WITH_LIMIT_OF

field-namestorage-area-name

 The name of the field that specifies what value will be used as a
 limit for partitioning the index across multiple storage areas.

 If the index key is multisegmented, you can include some or all of
 the fields that are joined to form the index key.  Separate multiple
 field names with commas.

 The name of the storage area you want the index stored in.  You must
 define this storage area with the DEFINE DATABASE statement before
 you refer to it in the store clause.

 If the index is a hashed index, the storage area must have a MIXED
 page format.

 The maximum value for the index key that will reside in the specified
 storage area.

 The number of literals in this clause must be the less than or equal
 to the number of fields in the USING clause.  Repeat this clause to
 partition the index entries among multiple storage areas.

 When you define a multisegmented index using multiple keys and use
 the STORE USING...WITH LIMITS clauses, if the values for the first
 key are all the same, then set the limit for the first key at that
 value.  By doing this, you ensure that the value of the second key
 determines the storage area in which each record will be stored.

 Note that the last storage area you specify CANNOT have a WITH LIMIT
 OF clause associated with it.

 sorted-index-param-list =

  ────┬────┬──────────────────>──────────────────────┬───┬─────────>
      │    ├─> 
N
O
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E 
S
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E ─────> number-bytes ────────┤   │
      │    ├─> 
P
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F
I
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L ──────> percentage ──────┤   │
      │    └─> 
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      │                       └─────> 
Q
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      │                                                  │
      └────────────────────<─────────────────────────────┘

Additional information available:

NODE-SIZEPERCENT-FILL

USAGE-mode

 The size of each index node.  The number and level of the resulting
 index nodes depend on this value, the number and size of the index
 keys, and the value of the PERCENT FILL clause.

 Sets the initial percentage of fullness for each node in the index
 structure.  The valid range is 1 to 100 percent.

 USAGE UPDATE, the default, sets the percent fullness of each index
 node at 70 percent.  USAGE QUERY sets this value at 100 percent.
 Supplying the PERCENT FILL and USAGE clause is allowed in the syntax;
 however, the USAGE option takes precedence over an explicit PERCENT
 FILL value.

 Specifies whether Rdb/VMS creates a B-tree index structure (SORTED),
 or a hashed index structure (HASHED).  If you specify HASHED, you
 cannot choose options from the sorted-index-param-list.  Hashed
 indexes are effective only for exact match retrievals.  Sorted
 indexes are effective for range retrievals.

 An optional keyword that causes Rdb/VMS to create ascending index
 segments.  ASCENDING is the default.  To sort records in a particular
 way in the result of a particular query, specify the sort order in
 the SORTED BY clause.

 An optional keyword that causes Rdb/VMS to create descending index
 segments.  To guarantee that records will be sorted in a particular
 way in the result of a particular query, specify the sort order in
 the SORTED BY clause.

 A compression clause that specifies that the "first n" characters of
 a certain key are to be used in the index.  These are specified with
 the DUPLICATES ARE ALLOWED clause.  For example, if you wanted to
 place an index on a 100 byte field that is generally unique to the
 first 20 bytes, you could specify the first 20 bytes and save as much
 as 80 bytes per entry.

 A compression clause for all-numeric fields that translates the field
 values into a more compactly encoded form.  You can mix mapped and
 unmapped fields, but the most storage space is gained by building
 indexes of multiple fields of data type WORD or LONGWORD.  Rdb/VMS
 attempts to pack all such fields into the smallest possible space.

 The "l" (low) to "h" (high) specifies the range of integers as the
 value of the index key.

 The valid range of the compressed key:

  o  Cannot be zero

  o  The range H - L is limited to (2**31) - 4 x (10**scale)

     If the value of the key is less than zero or greater than
     (2**31) - 4 x (10**scale), Rdb/VMS signals an exception.


 The following notes refer to compressed indexes:

 All text compressed indexes require the DUPLICATES ARE ALLOWED
 clause, which is the default for the DEFINE INDEX statement.  If the
 SIZE IS clause is specified, the field referred to by the clause must
 be of the TEXT or VARYING TEXT data type.  The field must also be the
 same length or greater in length than the value specified in the SIZE
 IS clause.

 For integer field compressed indexes, the index field must be of data
 type WORD or LONGWORD.  You can mix mapped and unmapped fields, but
 the most storage space is gained by building indexes of multiple
 fields of data type WORD or LONGWORD.  Rdb/VMS attempts to pack all
 such fields into the smallest possible space.

 Compressed key suffixes also enable the user to use fields longer
 than 254 characters as index keys.

 If any data values already stored are less than l or greater than h,
 the DEFINE INDEX statement will fail.

 A subsequent STORE or MODIFY operation that attempts to store a value
 less than l or greater than h will fail.

 Example 1

 The following example creates a simple relation index:

 DEFINE INDEX EMP_EMPLOYEE_ID FOR EMPLOYEES
   DUPLICATES ARE NOT ALLOWED.
     EMPLOYEE_ID.
  END EMP_EMPLOYEE_ID INDEX.

 This statement names the index and names the field to serve as the
 index key.

 The clause, DUPLICATES ARE NOT ALLOWED, causes Rdb/VMS to return an
 error message if a user attempts to store an identification number
 that is already assigned.


 Example 2

 The following example defines a hashed index, and uses the store
 clause to partition the index into different storage areas:

 DEFINE INDEX EMPLOYEES_HASH
   DESCRIPTION IS /* Hash index for employees */
   FOR EMPLOYEES
   DUPLICATES ARE NOT ALLOWED
   STORE USING EMPLOYEE_ID
    WITHIN
     EMPIDS_LOW WITH LIMIT OF "00200";
     EMPIDS_MID WITH LIMIT OF "00400";
     EMPIDS_OVER
   TYPE IS HASHED.
   EMPLOYEE_ID.
 END EMPLOYEES_HASH.

 Example 3

 The following example creates a multisegment index:

 DEFINE INDEX EMP_FULL_NAME FOR EMPLOYEES
    DUPLICATES ARE ALLOWED.
      LAST_NAME.
      FIRST_NAME.
      MIDDLE_INITIAL.
 END EMP_FULL_NAME INDEX.

 This statement names three fields.  Rdb/VMS concatenates these three
 fields to make the multisegment index key.


 Example 4

 The following example defines the EMP_EMPLOYEE_ID index and causes
 the LAST_NAME segment to be defined in DESCENDING order.

 DEFINE INDEX EMP_FULL_NAME FOR EMPLOYEES.
 LAST_NAME DESCENDING.
 FIRST_NAME ASCENDING.
 MIDDLE_INITIAL.
 END EMP_FULL_NAME INDEX.

 Having defined such an index on a particular field does not guarantee
 that Rdb/VMS will use that index in a particular query retrieval.  To
 ensure a particular sort order is returned by a particular query, you
 have to specify that order in the RSE:

 FOR E IN EMPLOYEES
     SORTED BY DESCENDING E.STATUS_CODE,
               ASCENDING E.LAST_NAME,
               DESCENDING E.EMPLOYEE_ID...



 Example 5

 The following example defines the JH_EMPLOYEE_ID index and sets each
 node size to 350 bytes and the initial fullness of each node to 50
 percent:

 DEFINE INDEX JH_EMPLOYEE_ID FOR JOB_HISTORY
     DUPLICATES ARE ALLOWED
     NODE SIZE 350
     PERCENT FILL 50.
         EMPLOYEE_ID.
 END JH_EMPLOYEE_ID INDEX.