case_value_expression ::= the expression evaluated by the simple When/Then CASE format.
when_expression ::= The expression to which case_value_expression is compared. The data types of case_value_expression and each when_expression must be the same or must be an implicit conversion.
then_expression ::= the expression returned when case_value_expression equals when_expression evaluates to TRUE.
else_expression ::= the expression returned if no comparison operation evaluates to TRUE. If this argument is omitted and no comparison operation evaluates to TRUE, CASE returns NULL.
search_expression ::= the Boolean expression evaluated by the searched CASE format. Search_expression may be any valid Boolean expression.