Executes one or more SQL statements conditionally. It then
    continues processing by executing any SQL statement that
    immediately follows the block.

1  –  Environment

    You can use the IF control statement in a compound statement:

    o  In interactive SQL

    o  Embedded in host language programs to be precompiled

    o  As part of a procedure in an SQL module

    o  In dynamic SQL as a statement to be dynamically executed

2  –  Format

  if-statement =

  -----> IF predicate THEN --+-> compound-use-statement -+--------+
                             +------------ <-------------+        |
  +---------------------------------------------------------------+
  ++-+--------------------------------------------------------+-+-+
   | +-> ELSEIF predicate THEN -+-> compound-use-statement -+-+ | |
   |                            +------------ <-------------+   | |
   +---------------------------- <------------------------------+ |
  +---------------------------------------------------------------+
  +--+----------------------------------------+--> END IF --------->
     +-> ELSE --+-> compound-use-statement -+-+
                +------------ <-------------+

3  –  Arguments

3.1  –  compound-use-statement

    See the Compound_Statement HELP topic for a description of the
    SQL statements that are valid in a compound statement.

3.2  –  END_IF

    Marks the end of an IF statement. Every IF statement must end
    with the END IF clause.

3.3  –  ELSE compound use statement

    Executes one or more SQL statements associated with the ELSE
    clause but only when the value of the IF and ELSEIF predicates
    evaluate to FALSE or UNKNOWN.

3.4  –  ELSEIF_THEN

    If the ELSEIF predicate evaluates to TRUE, SQL executes the SQL
    statements in the THEN clause. If the ELSEIF predicate does not
    evaluate to TRUE, SQL evaluates the predicates in any subsequent
    ELSEIF or ELSE clauses.

3.5  –  IF_THEN

    Executes one or more SQL statements in an IF . . . END IF block
    only when the value of an IF predicate evaluates to TRUE. A
    predicate, also called a conditional expression, specifies a
    condition that SQL evaluates to TRUE, FALSE, or UNKNOWN. If
    the predicate evaluates to TRUE, SQL executes the statement in
    the THEN clause. If the predicate does not evaluate to TRUE,
    SQL evaluates the predicate in any ELSEIF clauses. If the IF
    statement contains no ELSEIF clauses, SQL executes any statements
    in the ELSE clause.

3.6  –  predicate

    See the Predicates HELP topic for more information on predicates.

4  –  Examples

    Example 1: Using an IF control statement

    IF (SELECT COUNT (*) FROM STUDENTS
               WHERE CLASS = :CLASS_NUM)
         > 30

       THEN
          SET :MSG = 'Class is too large.';
       ELSE
          SET :MSG = 'Class size is O.K.';

    END IF;