MySql三种避免重复插入数据的方法

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。

1. insert ignore。
2. replace into
3. 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。

以上就是mysql四种避免重复插入数据的方法的详细内容，更多关于mysql 避免插入重复数据的资料请关注其它相关文章！