The IF statement can be used in a script to branch the execution based on a Boolean expression. The optional ELSE or ELSEIF clauses can be used to simulate the CASE … WHEN … control structure type.
IF condition_expr THEN
END IF | END | ENDIF;
statement_block :: statement | statement;
condition_expr ::= Boolean | FETCH cursor_name
elseif_clause_list ::= ELSEIF condition_expr THEN
Note that the condition_expr may be a regular Boolean expression or it may be a FETCH statement . The FETCH statement, when used in this context, evaluates to TRUE if the cursor is located on a valid row after the fetch operation; otherwise, it evaluates to FALSE. This provides a convenient method for testing the "end of file" condition when scrolling through a cursor.
The IF statement is similar to the general branching statement in other programming languages. If the condition_expr evaluates to TRUE, the statement_block after the THEN keyword is executed. The statement block is terminated when an ELSE, ELSEIF, ELIF or END keyword is encountered. If the condition_expr evaluates to FALSE, the execution jumps to the elseif_clause_list if present. If no elseif_clause_list is present but there is an ELSE section, the execution jumps to the ELSE section. If there is no elseif_clause_list and no ELSE section, the execution continues to the statement after the END [IF].
The execution of the elseif_clause is the same as the execution of a regular IF statement.
// A sample script demonstrates the IF statement
DECLARE dVal Double;
dVal = 3 * Rand();
IF dVal < 1 THEN
SELECT * FROM employees;
ELSEIF dVal < 2 THEN
dVal = dVal + 3;
SELECT * FROM employees WHERE empid > dVal;
UPDATE employees SET empid = empid + dVal;
dVal = dVal * dVal;
// A sample script demonstrates the IF statement using the FETCH result
DECLARE cursor1 CURSOR AS SELECT * FROM employees;
IF FETCH Cursor1 THEN
INSERT INTO ErrorLog ( msg ) VALUES ( 'employees is not empty' );