case_n

Evaluates "condition_expression_list" and returns the position of the first true condition, provided that no prior condition in the list evaluates to unknown. The keywords must be enclosed in curly brackets. No case is an optional condition that evaluates to true if every expression in the list evaluates to false. No case or unknown is an optional condition that evaluates to true if every expression in the list evaluates to false, or if an expression evaluates to unknown and all prior conditions in the list evaluate to false. Unknown is an optional condition that evaluates to true if an expression evaluates to unknown and all prior conditions in the list evaluate to false.

case_n ( condition_expression_list [ , NO CASE|UNKNOWN|NO CASE OR 
UNKNOWN [ , UNKNOWN ] ] )