一:IF-THEN语句
IF (condition) THEN commands; END IF;
二:IF-THEN_ELSE语句
IF (condition) THEN S1; ELSE S2; END IF;
三:IF-THEN—ELSEIF—ELSE
IF(boolean_expression 1)THEN S1; ELSIF( boolean_expression 2) THEN S2; ELSIF( boolean_expression 3) THEN S3; ELSE S4; END IF;
四:CASE语句
CASE selector WHEN 'value1' THEN S1; WHEN 'value2' THEN S2; WHEN 'value3' THEN S3; ... ELSE Sn; -- default case END CASE;
CASE WHEN selector = 'value1' THEN S1; WHEN selector = 'value2' THEN S2; WHEN selector = 'value3' THEN S3; ... ELSE Sn; -- default case END CASE;