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

 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.

 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.

 DEFINE INDEX name ───┬───────────────────────────────┬─────────┐
                      └─> 
D
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N typebox (I)typebox (S) typebox (/)typebox (*) text */ ──┘         │
 ┌─────────────────────────────<────────────────────────────────┘
 └─> Ftypebox (O)typebox (R) ────> relation-name ───┬──────────>────────────┬───────┐
                                └─> duplicates-clause ──┘       │
 ┌────────────────────────────────<─────────────────────────────┘
 └─┬───────────>─────────────┬──────────>───────────────────────┐
   └─> index-store-clause ───┘                                  │
 ┌─────────────────────────────────<────────────────────────────┘
 └─┬─────────────>───────────────┬───────────────────────────┬──┐
   ├─> 
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   │             └───> 
S
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D ──> sorted-index-param-list ───┤  │
   └──────────────> sorted-index-param-list ─────────────────┘  │
 ┌───────────────────────── . <─────────────────────────────────┘
 └┬┬> field-name ┬┬───────>─────┬┬─> 
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  │└──────<──────┘├> 
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  │               └> 
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  └────────────── . <────────────┘

Additional information available:

TYPE_IS

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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T
H
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N ────> storage-area-name ─────────────>─────────┬─>
 ┌──────┘                                                          │
 │                                                                 │
 └─────> 
U
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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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H 
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T typebox (O)F ─┬> literal ─┬─ typebox (;) ─┬─┐  │
   │                                        └──── , <───┘     │ │  │
   └───────────────────────────<──────────────────────────────┘ │  │
 ┌─────────────────────────────<────────────────────────────────┘  │
 │                                                                 │
 └─────────────────────> 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 insure 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
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E 
S
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E ─────> number-bytes ────────┤   │
      │    ├─> 
P
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F
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L ──────> percentage ──────┤   │
      │    └─> 
U
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E ─────────┬─────> 
U
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D
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E ───┬────┘   │
      │                       └─────> 
Q
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R
Y ────┘        │
      │                                                  │
      └────────────────────<─────────────────────────────┘

Additional information available:

NODE-SIZEPERCENT-FILLDESCENDING

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.

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

 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.

 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.