Preface
In the case of MySql primary key conflict or unique key conflict, according to the insertion method, there are generally the following four insertion methods to avoid errors.
insert ignore。
replace into
insert on duplicate key update
insert ignore
insert ignore will ignore the data that already exists in the database. According to the primary key or unique index, if there is no data in the database, new data will be inserted. If there is data, it will be skipped.
Small case:
Table Structure
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)
Insert conflicting data
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
View Results
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 will try to insert data first, and delete it if conflicts are found. Otherwise, do nothing.
Small 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)
Insert conflicting data
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)
You can see that the original record is gone, and the new record is there.
insert on duplicate key update
If insert on duplicate key update is specified at the end of the insert into statement, if there are duplicate values, the update will be performed after the duplicate values appear.
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)
Insert a piece of data that conflicts with the unique key (column c1) of record id=3
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)
You can see that the record with id=3 has changed, c1=the original c1+3, and the other columns have not changed.
There is no way, but the technique can be achieved; if there is no way, it ends with the technique
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