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mysql添加唯一索引语句(mysql查看表字段命令)
2022-11-06 08:08

当MySQL表字段设置unique key或者primary key时,被约束的字段就必须是唯一的。新插入数据直接使用insert into,如果出现唯一性冲突,就会抛出异常。我们可以根据需求选择合适的插入语句。

为了演示,我们先新建一张user表,SQL语句如下,其中user_id为主键,username为唯一索引

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user`  (
  `user_id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '用户id',
  `username` varchar(64) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '用户名',
  `password` varchar(64) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '密码',
  `mobile_phone_number` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '手机号码',
  `email` varchar(64) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '邮箱',
  `delete_state` tinyint(1) UNSIGNED DEFAULT 0 COMMENT '用户状态,1表示删除,0表示未删除',
  `create_time` datetime(0) DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
  `update_time` datetime(0) DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP(0) COMMENT '更新时间',
  PRIMARY KEY (`user_id`) USING BTREE,
  UNIQUE INDEX `uk_username`(`username`) USING BTREE COMMENT '用户名唯一'
) ENGINE = InnoDB AUTO_INCREMENT = 9 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES (1, 'JourWon', '123456', '13800000000', '[email protected]', 0, CURRENT_TIMESTAMP, NULL);
INSERT INTO `user` VALUES (2, '马云', '123456', '13800000011', '[email protected]', 0, CURRENT_TIMESTAMP, NULL);
INSERT INTO `user` VALUES (3, '马化腾', '123456', '13800000022', '[email protected]', 0, CURRENT_TIMESTAMP, NULL);
INSERT INTO `user` VALUES (4, '李彦宏', '123456', '13800000033', '[email protected]', 0, CURRENT_TIMESTAMP, NULL);
INSERT INTO `user` VALUES (5, '任正非', '123456', '13800000044', '[email protected]', 0, CURRENT_TIMESTAMP, NULL);
INSERT INTO `user` VALUES (6, 'Jobs', '123456', '13800000055', '[email protected]', 0, CURRENT_TIMESTAMP, NULL);
INSERT INTO `user` VALUES (7, 'Bill Gates', '123456', '13800000066', 'Bill [email protected]', 0, CURRENT_TIMESTAMP, NULL);
INSERT INTO `user` VALUES (8, 'Buffett', '123456', '13800000077', '[email protected]', 0, CURRENT_TIMESTAMP, NULL);

SET FOREIGN_KEY_CHECKS = 1;

常用插入语句

insert into

当插入数据时,如果唯一性校验出现重复问题,则报错;

如果没有重复性问题,则执行插入操作。

简单总结:重复则报错,不重复则插入。

示例

INSERT INTO `user`
VALUES
	( 8, 'Buffett', '123456', '13800000077', '[email protected]', 0, CURRENT_TIMESTAMP, NULL );

执行结果

INSERT INTO `user`
VALUES
	( 8, 'Buffett', '123456', '13800000077', '[email protected]', 0, CURRENT_TIMESTAMP, NULL )
> 1062 - Duplicate entry '8' for key 'user.PRIMARY'
> 时间: 0.001s

insert into … on duplicate key update

当插入数据时,如果唯一性校验出现重复问题,则在原有记录基础上,更新指定字段内容,其它字段内容保留;

如果没有重复性问题,则执行插入操作。

简单总结:重复则更新指定字段,不重复则插入

示例

INSERT INTO `user` ( username, PASSWORD, mobile_phone_number, email )
VALUES
	( 'Buffett', '123456', '13800000088', '[email protected]' ) 
	ON DUPLICATE KEY UPDATE mobile_phone_number = '13800000088';

执行结果

INSERT INTO `user` ( username, PASSWORD, mobile_phone_number, email )
VALUES
	( 'Buffett', '123456', '13800000088', '[email protected]' ) 
	ON DUPLICATE KEY UPDATE mobile_phone_number = '13800000088'
> Affected rows: 2
> 时间: 0.022s

表记录,mobile_phone_number更新了,update_time也有值了,但是user_id没有变

replace into

replace into表示插入替换数据,当插入数据时,如果唯一性校验出现重复问题,删除旧记录,插入新记录;

如果没有重复性问题,则执行插入操作,效果和insert into是一样的。

简单总结:重复则先删除再插入新记录,不重复则插入

示例

REPLACE INTO `user` ( username, PASSWORD, mobile_phone_number, email )
VALUES
	( 'Buffett', '123456', '13800000099', '[email protected]' );

执行结果

REPLACE INTO `user` ( username, PASSWORD, mobile_phone_number, email )
VALUES
	( 'Buffett', '123456', '13800000099', '[email protected]' )
> Affected rows: 2
> 时间: 0.019s

表记录,user_id和mobile_phone_number变了,update_time变为了空

使用场景总结

如果出现重复异常,希望捕获异常,则使用insert into

如果出现重复异常,希望保存旧纪录,忽略新纪录,则使用insert ignore into

如果出现重复异常,希望更新指定字段,则使用insert into … on duplicate key update

如果出现重复异常,希望删除旧记录,插入新记录,则使用replace into

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