A phrase that defines specific conditions that individual records
 must meet before Rdb/VMS includes them in a record stream.  A record
 stream is a temporary group of related records that satisfy the
 conditions you specify in the record selection expression.  A record
 stream can consist of:

  o  All the records of one or more relations

  o  A subset of the records in one or more relations

 The following sections describe how to use the record selection
 expression to form record streams.

Additional information available:

FormatExamples

 rse =

 ──┬───────────────────┬───> relation-clause ──┬──────────────────┬─┐
   └──> first-clause ──┘                       └─> cross-clause ──┘ │
                                                                    │
  ┌─────────────────────────────────────────────────────────────────┘
  └┬──────────────────┬─┬────────────────────┬─┬──────────────────┬──>
   └──> with-clause ──┘ └──> reduce-clause ──┘ └──> sort-clause ──┘

Additional information available:

first-clauserelation-clausewith-clausesort-clausereduce-clausecross-clause

 first-clause =

   ──────>  
F
I
R
S
T  ────>  value-expr  ──────>

 Specifies how many records are in the record stream formed by the
 record selection expression.  If you include the element FIRST n, the
 record stream has no more than n records.  The argument n should be a
 positive integer or a value expression that evaluates to a positive
 integer.  For more information on value expressions, ask for HELP on
 Value_expr.

Additional information available:

More

 Note the following rules:

  o  Rdb/VMS does not guarantee the order of records in a record
     stream unless you specify a sort order.  For this reason, when
     you use FIRST n in the RSE, the actual records in the record
     stream are unpredictable.  Therefore, you should always specify
     SORT when you use FIRST n.

  o  If n evaluates to zero or a negative number, the record stream
     will be empty.

  o  If you specify FIRST n and n is greater than the number of
     records satisfying those conditions, the record stream consists
     of all records meeting the conditions of the record selection
     expression.

  o  If n is not an integer, Rdb/VMS rounds any fractional part of the
     value and uses the remaining integer as the number of records in
     the record stream.

 relation-clause =

 ──> context-var ───> 
I
N ──┬─────────────────────┬──> relation-name ──>
                           └──> db-handle ──> . ─┘

 In the relation-clause, you must declare context variables for a
 record stream or a loop.  A context variable is a temporary name that
 identifies the record stream to Rdb/VMS.

 Once you have associated a context variable with a relation, you use
 the context variable to refer to fields from that relation.  In this
 way, Rdb/VMS always knows which field from which relation you are
 referring to.

 You must use a context variable in every data manipulation statement
 and in every data definition statement that uses an RSE.

 If you access several record streams at once, the context variable
 lets you distinguish between fields from different record streams,
 even if different fields have the same name.

 In all programs except RDBPRE, RDML, SQL$PRE, and SQL$MOD programs,
 context variables must be unique within a request.

 with-clause =

   ──────> 
W
I
T
H ───> conditional-expr ───>

 Allows you to specify conditions that must be true for a record to be
 included in a record stream.  Ask for HELP on Cond_expr for more
 details.

 sort-clause =

 ───> 
S
O
R
T
E
D 
B
Y ───┬─┬────────────────┬──> value-expr ──┬──>
                   │ ├──> 
A
S
C
E
N
D
I
N
G ──┤                 │
                   │ └──> 
D
E
S
C
E
N
D
I
N
G ─┘                 │
                   └────────────── , <──────────────────┘

 Lets you sort the records in the record stream on one or more value
 expressions (sort keys).  The default order is ASCENDING.  Rdb/VMS
 uses sort keys in the order you name them.  Missing field values are
 placed last.  A sort key can be any Rdb/VMS value expression.  For
 more information on value expressions, as for HELP on Value_expr.

 reduce-clause =

   ─────> 
R
E
D
U
C
E
D 
T
O ───┬──> value-expr ─────┬───>
                        └──────<──── , ──<───┘

 Lets you eliminate duplicate values for fields in a record stream.
 You can use this expression to eliminate redundancy in the results of
 a query and to group the records in a relation according to a field
 value.  Rdb/VMS does not guarantee the sorting order of the resulting
 record stream.  To assure the desired order use the SORTED BY clause.
 If you use the REDUCED clause, you should retrieve only the fields
 that you specify in the list of value expressions.  If you retrieve
 other fields, the results are unpredictable.

 cross-clause =

 ─┬─> 
C
R
O
S
S ──> relation-clause ─┬────────────────────────────┬─┬──>
  │                              └──> 
O
V
E
R ─┬─> field-name ─┬─┘ │
  │                                         └────── , <─────┘   │
  └──────────────────────────────<──────────────────────────────┘

 Lets you combine records from two or more record streams.  You can
 join these records in combinations based on the relationship between
 the values of fields in the separate record streams.  This combining
 of records is called a relational join.

 Choose the clause of the RSE you want to see from the following list.

Additional information available:

FIRSTSORTREDUCEDCROSSVIEWS

relation-clause

 Example 1

 Print the first ten records in a relation:

 RDO> FOR FIRST 10 E IN EMPLOYEES
 cont>   SORTED BY E.LAST_NAME
 cont> PRINT E.*
 cont> END_FOR


 Example 2

 Use FIRST and SORTED BY to find the maximum values for a field:

 RDO> FOR FIRST 5 C IN CURRENT-SALARY
 cont>    SORTED BY C.SALARY_AMOUNT
 cont> PRINT
 cont>    C.FIRST-NAME,
 cont>    C.LAST-NAME
 cont> END_FOR


 Example 3

 Use FIRST with a value expression:

 &RDB&  GET TENTH = ( COUNT OF E IN EMPLOYEES / 10 )

 &RDB&  START_TRANSACTION READ_WRITE
 &RDB&  FOR FIRST TENTH E IN EMPLOYEES
              SORTED BY E. LAST_NAME
               .
               .
               .

 Example 1

 Use ERASE:

     RDO> FOR E IN EMPLOYEES WITH E.EMPLOYEE_ID = "00334"
     cont> ERASE E
     cont> END_FOR

     Example 2

 Use MODIFY:

     &RDB&  FOR SH IN SALARY_HISTORY
     &RDB&        WITH SH.EMPLOYEE_ID = ID-NUMBER
     &RDB&        AND SH.SALARY_END MISSING
     &RDB&        MODIFY SH USING
     &RDB&          SH.SALARY_AMOUNT =
     &RDB&          ( SH.SALARY_AMOUNT + ( 1000 * RATING ) )
     &RDB&        END_MODIFY
     &RDB&      END_FOR

     Example 3

 Use STORE:

     &RDB&  STORE D IN DEPARTMENTS USING
     &RDB&          D.DEPARTMENT_NAME = "Recreation";
     &RDB&          D.DEPARTMENT_CODE = "RECR";
     &RDB&          D.MANAGER_ID = "00445"
     &RDB&      END_STORE

     Example 4

 Use two record streams:

     &RDB&  FOR E IN EMPLOYEES CROSS
     &RDB&        J IN JOB_HISTORY WITH
     &RDB&        E.EMPLOYEE_ID = J.EMPLOYEE_ID

 RDO> FOR E IN EMPLOYEES SORTED BY E.BIRTHDAY

 Because this example did not specify the sort order, Rdb/VMS
 automatically sorts the EMPLOYEES records in ASCENDING order by
 BIRTHDAY.


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

 If you do not specify ASCENDING or DESCENDING for the second or
 subsequent sort keys, Rdb/VMS uses the order you specified for the
 preceding sort key.

 FOR J IN JOB_HISTORY
    WITH J.JOB_END MISSING
    REDUCED TO J.JOB_CODE
    SORTED BY J.JOB_CODE
 PRINT J.JOB_CODE
 END_FOR

 This example lists all the currently active job codes.  It includes
 each value in the record stream only once.

 Create a list of employees and their current salary.

 FOR E IN EMPLOYEES CROSS
   SH IN SALARY_HISTORY
     OVER EMPLOYEE_ID WITH
       SH.SALARY_END MISSING
 PRINT E.LAST_NAME,
       SH.SALARY_AMOUNT
 END_FOR

 The EMPLOYEES relation contains, among other things, the name and
 employee ID of each employee.  The SALARY_HISTORY relation contains a
 SALARY_AMOUNT for each salary level each employee has attained and
 the starting and ending date for each current salary.  For the
 current salary, the salary ending date is missing.  These relations
 share the common field, EMPLOYEE_ID.  Therefore, you can use CROSS to
 join them over this field.

 This view definition incorporates an RSE that includes a CROSS
 operation.

 DEFINE VIEW CURRENT_JOB OF JH IN JOB_HISTORY
   CROSS E IN EMPLOYEES OVER EMPLOYEE_ID
      WITH JH.JOB_END MISSING.
       E.LAST_NAME.
       E.FIRST_NAME.
       E.EMPLOYEE_ID.
       JH.JOB_CODE.
       JH.DEPARTMENT_CODE.
       JH.SUPERVISOR_ID.
       JH.JOB_START.
       JH.JOB_END.
 END VIEW.