General CASE Statement (searched_case_statement) 
The general CASE statement (searched_case_statement) is a syntax element that can be used in a routine to define a database procedure (see CREATE DBPROC[EDURE] statement), a database function (see CREATE FUNCTION statement), or a trigger (see CREATE TRIGGER statement).
Structure
Syntax
<searched_case_statement> ::= CASE <searched_case_when_clause>... [<case_else_clause>] END [CASE] <searched_case_when_clause> ::= WHEN <search_condition> THEN <statement>; <case_else_clause> ::= ELSE <statement>;
Explanation
A CASE statement (case_statement) allows the conditional execution of a statement depending on search conditions or equality of operands.
For a general CASE statement (searched_case_statement), the first fulfilled search condition is determined, the associated statement executed, and the CASE statement then ended.
Example
CASE
WHEN digit = 0 THEN toCHAR = 'zero';
WHEN digit = 1 THEN toCHAR = 'one';
WHEN digit = 2 THEN toCHAR = 'two';
WHEN digit = 3 THEN toCHAR = 'three';
WHEN digit = 4 THEN toCHAR = 'four';
WHEN digit = 5 THEN toCHAR = 'five';
WHEN digit = 6 THEN toCHAR = 'six';
WHEN digit = 7 THEN toCHAR = 'seven';
WHEN digit = 8 THEN toCHAR = 'eight';
WHEN digit = 9 THEN toCHAR = 'nine';
ELSE STOP(-29000, 'no digit');
END CASE
If no matching literal or fulfilled search condition exists in a CASE statement, the statement defined in the ELSE branch is executed.
If there is no ELSE branch, the runtime error -28901 is returned.