Using SELECT Statements

The SELECT statement defines a set of conditional execution statements. This statement has two formats: format-1 and format-2. Format-1 has an implied = operator between the SELECT variable and the WHEN value, as follows:

SELECT   ( variable )
   WHEN  ( constant )
         statement
   WHEN  ( constant or
         filtlist_name )
         statement
   OTHERWISE
         statement
   END

A format-2 SELECT statement has no select variable:

SELECT
   WHEN  (  condition )
         statement
   WHEN  (  condition )
         statement
   OTHERWISE
         statement
   END

All IBM-supplied ACS environment conditions are tested by the WHEN clauses. The comment, /* INSTALLATION EXIT */, indicates that the OTHERWISE clause is run only if an installation exit has set &ACSENVIR to a value you defined in an ACS routine exit. Figure 1 shows a format-1 SELECT statement with the select variable ACSENVIR:

Figure 1. Example of the Format-1 SELECT Statement

SELECT   (&ACSENVIR)
    WHEN  ('ALLOC')
         DO    ...    END
    WHEN  ('RECALL')
         DO    ...    END
    WHEN  ('RECOVER')
         DO    ...    END
    WHEN  ('CONVERT')
         DO    ...    END
    OTHERWISE  /* INSTALLATION EXIT */
         DO    ...    END
END

When coding ACS routines, remember that the WHEN clauses of the SELECT statement are tested serially. The first WHEN that is true causes its clause to be run. After the first true WHEN is encountered, the rest of the SELECT is not run. Figure 2 shows a format-2 SELECT statement:

Figure 2. Example of the Format-2 SELECT Statement

SELECT
    WHEN  (&RETPD  <  7)
         SET &MGMTCLAS  = 'DELSOON'
    WHEN  (&RETPD  <  30)
         SET &MGMTCLAS  = 'FREQBKUP'
    WHEN  (&RETPD  <  60)
         SET &MGMTCLAS  = 'NORMAL'
    OTHERWISE
         SET &MGMTCLAS  = 'DELNEVER'
END