CASE case_value
    WHEN when_value THEN statement_list
    [WHEN when_value THEN statement_list] ...
    [ELSE statement_list]
END CASE

Or:

CASE
    WHEN search_condition THEN statement_list
    [WHEN search_condition THEN statement_list] ...
    [ELSE statement_list]
END CASE

The CASE statement for stored routines implements a complex conditional construct. If a search_condition evaluates to true, the corresponding SQL statement list is executed. If no search condition matches, the statement list in the ELSE clause is executed. Each statement_list consists of one or more statements.

Note: The syntax of the CASE statement shown here for use inside stored routines differs slightly from that of the SQL CASE expression described in Section 12.3, “Control Flow Functions”. The CASE statement cannot have an ELSE NULL clause, and it is terminated with END CASE instead of END.