正如我在本文中所解释的，从8.0.16版本开始，MySQL添加了对CHECK约束的支持：

ALTER TABLE topic ADD CONSTRAINT post_content_check CHECK ( CASE WHEN DTYPE = 'Post' THEN CASE WHEN content IS NOT NULL THEN 1 ELSE 0 END ELSE 1 END = 1 );

ALTER TABLE topic ADD CONSTRAINT announcement_validUntil_check CHECK ( CASE WHEN DTYPE = 'Announcement' THEN CASE WHEN validUntil IS NOT NULL THEN 1 ELSE 0 END ELSE 1 END = 1 ); 以前，仅在使用BEFORE INSERT和BEFORE UPDATE触发器时才可用：

CREATE TRIGGER post_content_check BEFORE INSERT ON topic FOR EACH ROW BEGIN IF NEW.DTYPE = 'Post' THEN IF NEW.content IS NULL THEN signal sqlstate '45000' set message_text = 'Post content cannot be NULL'; END IF; END IF; END;

CREATE TRIGGER post_content_update_check BEFORE UPDATE ON topic FOR EACH ROW BEGIN IF NEW.DTYPE = 'Post' THEN IF NEW.content IS NULL THEN signal sqlstate '45000' set message_text = 'Post content cannot be NULL'; END IF; END IF; END;

CREATE TRIGGER announcement_validUntil_check BEFORE INSERT ON topic FOR EACH ROW BEGIN IF NEW.DTYPE = 'Announcement' THEN IF NEW.validUntil IS NULL THEN signal sqlstate '45000' set message_text = 'Announcement validUntil cannot be NULL'; END IF; END IF; END;

CREATE TRIGGER announcement_validUntil_update_check BEFORE UPDATE ON topic FOR EACH ROW BEGIN IF NEW.DTYPE = 'Announcement' THEN IF NEW.validUntil IS NULL THEN signal sqlstate '45000' set message_text = 'Announcement validUntil cannot be NULL'; END IF; END IF; END; 有关使用8.0.16之前的MySQL版本的数据库触发器模拟CHECK约束的更多详细信息，请参阅本文。来源：stack overflow