用mysql创建两个表用户表包括username varchar64password varchar64 contactable bit1contacts int；联系人表包括username varchar64contact varchar64username和contact作为联合主键username和contact都参考用户表的username更新和删除时执行同样的操作；再用mysql创建一

如果更新成功，就输出一条成功提示信息。

用户表创建代码：

CREATE TABLE users ( username varchar(64) PRIMARY KEY, password varchar(64), contactable bit(1), contacts int );

联系人表创建代码：

CREATE TABLE contacts ( username varchar(64), contact varchar(64), PRIMARY KEY (username, contact), FOREIGN KEY (username) REFERENCES users(username) ON UPDATE CASCADE ON DELETE CASCADE, FOREIGN KEY (contact) REFERENCES users(username) ON UPDATE CASCADE ON DELETE CASCADE );

触发器1代码：

CREATE TRIGGER insert_contact BEFORE INSERT ON contacts FOR EACH ROW BEGIN DECLARE contactable_value bit; SELECT contactable INTO contactable_value FROM users WHERE username = NEW.contact; IF contactable_value = 0 THEN SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Contact is not contactable'; END IF; END;

触发器2代码：

CREATE TRIGGER update_contacts AFTER INSERT ON contacts FOR EACH ROW BEGIN UPDATE users SET contacts = contacts + 1 WHERE username = NEW.username OR username = NEW.contact; IF ROW_COUNT() > 0 THEN SELECT 'Contacts updated successfully'; END IF; END;