前言

MySql 在存在主键冲突或唯一键冲突的情况下，根据插入方式，一般有以下三种插入方式避免错误。

insert ignore。

replace into

insert on duplicate key update

insert ignore

insert ignore 会忽视数据库中已经存在的数据，根据主键或者唯一索引判断，如果数据库没有数据，就会插入新的数据，如果有数据的话就跳过这条数据

小case

表结构

root:test> show create table t3G

*************************** 1. row ***************************

Table: t3

Create Table: CREATE TABLE `t3` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`c1` int(11) DEFAULT NULL,

`c2` varchar(20) DEFAULT NULL,

`c3` int(11) DEFAULT NULL,

PRIMARY KEY (`id`),

UNIQUE KEY `uidx_c1` (`c1`)

) ENGINE=InnoDB AUTO_INCREMENT=18 DEFAULT CHARSET=utf8

1 row in set (0.00 sec)

root:test> select * from t3;

+----+------+------+------+

| id | c1 | c2 | c3 |

+----+------+------+------+

| 1 | 1 | a | 1 |

| 2 | 2 | a | 1 |

| 8 | NULL | NULL | 1 |

| 14 | 4 | bb | NULL |

| 17 | 5 | cc | 4 |

+----+------+------+------+

5 rows in set (0.00 sec)

插入冲突数据

root:test> insert ignore into t3 (c1,c2,c3) values(5,'cc',4),(6,'dd',5); Query OK, 1 row affected, 1 warning (0.01 sec)

Records: 2 Duplicates: 1 Warnings: 1

查看结果

root:test> show warnings;

+---------+------+---------------------------------------+

| Level | Code | Message |

+---------+------+---------------------------------------+

| Warning | 1062 | Duplicate entry '5' for key 'uidx_c1' |

+---------+------+---------------------------------------+

1 row in set (0.00 sec)

root:test> select * from t3;

+----+------+------+------+

| id | c1 | c2 | c3 |

+----+------+------+------+

| 1 | 1 | a | 1 |

| 2 | 2 | a | 1 |

| 8 | NULL | NULL | 1 |

| 14 | 4 | bb | NULL |

| 17 | 5 | cc | 4 |

| 18 | 6 | dd | 5 |

+----+------+------+------+

6 rows in set (0.00 sec)

replace into

replace into 会尝试先插入数据，如果发现冲突进行删除。否则不做任何操作。

小case

root:test> show create table t3G

*************************** 1. row ***************************

Table: t3

Create Table: CREATE TABLE `t3` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`c1` int(11) DEFAULT NULL,

`c2` varchar(20) DEFAULT NULL,

`c3` int(11) DEFAULT NULL,

PRIMARY KEY (`id`),

UNIQUE KEY `uidx_c1` (`c1`)

) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8

1 row in set (0.00 sec)

root:test> select * from t3;

+----+------+--------+------+

| id | c1 | c2 | c3 |

+----+------+--------+------+

| 1 | 1 | cc | 4 |

| 2 | 2 | dd | 5 |

| 3 | 3 | qwewqe | 3 |

+----+------+--------+------+

3 rows in set (0.00 sec)

插入冲突数据

root:test> replace into t3 (c1,c2,c3) values(3,'new',8);

Query OK, 2 rows affected (0.02 sec)

root:test> select * from t3;

+----+------+------+------+

| id | c1 | c2 | c3 |

+----+------+------+------+

| 1 | 1 | cc | 4 |

| 2 | 2 | dd | 5 |

| 4 | 3 | new | 8 |

+----+------+------+------+

3 rows in set (0.00 sec)

可以看到原有的记录已经没有了，新的记录又有了。

insert on duplicate key update

如果在insert into 语句末尾指定了 insert on duplicate key update 如果出现了重复值，则会在出现重复值以后进行update。

case

root:test> show create table t3G

*************************** 1. row ***************************

Table: t3

Create Table: CREATE TABLE `t3` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`c1` int(11) DEFAULT NULL,

`c2` varchar(20) DEFAULT NULL,

`c3` int(11) DEFAULT NULL,

PRIMARY KEY (`id`),

UNIQUE KEY `uidx_c1` (`c1`)

) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8

1 row in set (0.00 sec)

root:test> select * from t3;

+----+------+------+------+

| id | c1 | c2 | c3 |

+----+------+------+------+

| 1 | 1 | fds | 4 |

| 2 | 2 | ytu | 3 |

| 3 | 3 | czx | 5 |

+----+------+------+------+

3 rows in set (0.00 sec)

插入一条与记录id=3存在唯一键(列c1)冲突的数据

root:test> insert into t3(c1,c2,c3) values (3,'new',5) on duplicate key update c1=c1+3;

Query OK, 2 rows affected (0.01 sec)

root:test> select * from t3;

+----+------+------+------+

| id | c1 | c2 | c3 |

+----+------+------+------+

| 1 | 1 | fds | 4 |

| 2 | 2 | ytu | 3 |

| 3 | 6 | czx | 5 |

+----+------+------+------+

3 rows in set (0.00 sec)

可以看到，id=3的记录发生了改变，c1=原有的c1+3,其他列没有改变。

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