CASE value_expression_1 when_clause [...] [ ELSE scalar_expression_m ] END
- An expression whose value is tested for equality with value_expression_n.
WHEN value_expression_n THEN scalar_expression_n
- An expression whose value is returned if evaluation falls through to the ELSE clause.
- A set of expressions against which the value for value_expression_1 is tested for equality.
- An expression whose value is returned on the first equality comparison of value_expression_1 and value_expression_n.