The IF-THEN-ELSE statement can only be issued from within the body of a database procedure.

A Boolean expression (boolean_expr) must always evaluate to true or false. A Boolean expression can include comparison operators ('=', '<>', and so on) and the logical operators and, or, not. Boolean expressions involving nulls can evaluate to unknown. Any Boolean expression whose result is unknown is treated as if it evaluated to false.

If an error occurs during the evaluation of an if statement condition, the database procedure terminates and control returns to the calling application. This is true for both nested and non-nested if statements.