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，一般有以下四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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