1? label:
2 CASE
3 simple-when-clause
3 searched-when-clause
4? else-clause
5 END CASE

simple-when-clause:

1 expression
2+ 
2 WHEN expression THEN
2.1+ 
2.1 SQL-procedure-statement  ;

searched-when-clause:

1+ 
1 WHEN search-condition THEN
1.1+ 
1.1 SQL-procedure-statement  ;

else-clause:

1 ELSE
2+ 
2 SQL-procedure-statement  ;