在 MySQL 中，IGNORE 是一种在插入或更新数据时处理冲突的选项。具体来说，在 INSERT | UPDATE 语句中，IGNORE 的作用是在插入或更新数据时忽略特定的错误，而不导致整个操作失败。另外，IGNORE 选项还可以在非空约束、写入的字段内容超过字段长度时进行截断处理等，下面是几个具体的例子。
一、主键或唯一键冲突
1、初始化测试表并初始化数据
mysql> create table test1(id int not null primary key,
card_no varchar(10) not null,
name varchar(20) not null,
c1 varchar(2) ,
unique key uq_card_no(card_no)
);
Query OK, 0 rows affected (0.05 sec)
mysql> insert into test1(id,card_no,name,c1)
values(1,'1000000000','abc','a')
Query OK, 1 row affected (0.01 sec)
mysql> select * from test1;
+----+------------+------+------+
| id | card_no | name | c1 |
+----+------------+------+------+
| 1 | 1000000000 | abc | a |
+----+------------+------+------+
1 row in set (0.00 sec)
2、主键冲突
插入一个表中已存在的主键数据时，如果不添加ignore，则会报主键冲突。
mysql> insert into test1(id,card_no,name,c1) values(1,'1000000001','abc','a');
ERROR 1062 (23000): Duplicate entry '1' for key 'test1.PRIMARY'加上ignore选项后，结果如下：
mysql> select * from test1;
+----+------------+------+------+
| id | card_no | name | c1 |
+----+------------+------+------+
| 1 | 1000000000 | abc | a |
+----+------------+------+------+
1 row in set (0.00 sec)
mysql> insert ignore into test1(id,card_no,name,c1) values(1,'1000000001','abc','a'),
-> (2,'1000000001','ttt','b');
Query OK, 1 row affected, 1 warning (0.01 sec)
Records: 2 Duplicates: 1 Warnings: 1
mysql> show warnings;
+---------+------+---------------------------------------------+
| Level | Code | Message |
+---------+------+---------------------------------------------+
| Warning | 1062 | Duplicate entry '1' for key 'test1.PRIMARY' |
+---------+------+---------------------------------------------+
1 row in set (0.00 sec)
mysql> select * from test1;
+----+------------+------+------+
| id | card_no | name | c1 |
+----+------------+------+------+
| 1 | 1000000000 | abc | a |
| 2 | 1000000001 | ttt | b |
+----+------------+------+------+
2 rows in set (0.00 sec)
可以看到，有1条记录冲突，但是进行了warning提示，然后继续进行其他无冲突项的处理。
如果需查看warning信息，可以使用 show warnings 命令查看。
3、唯一键冲突
继续以上的表，先正常方式插入一条唯一键已存在的记录。
mysql> select * from test1;
+----+------------+------+------+
| id | card_no | name | c1 |
+----+------------+------+------+
| 1 | 1000000000 | abc | a |
| 2 | 1000000001 | ttt | b |
+----+------------+------+------+
2 rows in set (0.00 sec)
mysql> insert into test1(id,card_no,name,c1) values (4,'1000000000','ccccc','a');
ERROR 1062 (23000): Duplicate entry '1000000000' for key 'test1.uq_card_no'
mysql> select * from test1;
+----+------------+------+------+
| id | card_no | name | c1 |
+----+------------+------+------+
| 1 | 1000000000 | abc | a |
| 2 | 1000000001 | ttt | b |
+----+------------+------+------+
2 rows in set (0.00 sec)可见，因为报错，数据未插入。
下面通过添加ignore批量插入数据。
mysql> select * from test1;
+----+------------+------+------+
| id | card_no | name | c1 |
+----+------------+------+------+
| 1 | 1000000000 | abc | a |
| 2 | 1000000001 | ttt | b |
+----+------------+------+------+
2 rows in set (0.00 sec)
mysql> insert ignore into test1(id,card_no,name,c1) values
-> (4,'1000000000','ccccc','a'),
-> (5,'1000000003','ccccabc','a');
Query OK, 1 row affected, 1 warning (0.00 sec)
Records: 2 Duplicates: 1 Warnings: 1
mysql> show warnings;
+---------+------+---------------------------------------------------------+
| Level | Code | Message |
+---------+------+---------------------------------------------------------+
| Warning | 1062 | Duplicate entry '1000000000' for key 'test1.uq_card_no' |
+---------+------+---------------------------------------------------------+
1 row in set (0.00 sec)
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 1 | 1000000000 | abc | a |
| 2 | 1000000001 | ttt | b |
| 5 | 1000000003 | ccccabc | a |
+----+------------+---------+------+
3 rows in set (0.00 sec)
mysql>
可见，和主键冲突类似，有冲突的数据将会忽略告警而继续进行后续操作。
4、update操作
除了insert可以搭配ignore选项，update也可以添加ignore选项，例如：
更新主键：
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 1 | 1000000000 | abc | a |
| 2 | 1000000001 | ttt | b |
| 5 | 1000000003 | ccccabc | a |
+----+------------+---------+------+
3 rows in set (0.00 sec)
mysql> update test1 set id = id +1;
ERROR 1062 (23000): Duplicate entry '2' for key 'test1.PRIMARY'
mysql> update ignore test1 set id = id +1;
Query OK, 2 rows affected, 1 warning (0.01 sec)
Rows matched: 3 Changed: 2 Warnings: 1
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 1 | 1000000000 | abc | a |
| 3 | 1000000001 | ttt | b |
| 6 | 1000000003 | ccccabc | a |
+----+------------+---------+------+
3 rows in set (0.00 sec)
mysql>
更新唯一键：
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 1 | 1000000000 | abc | a |
| 3 | 1000000001 | ttt | b |
| 6 | 1000000003 | ccccabc | a |
+----+------------+---------+------+
3 rows in set (0.00 sec)
mysql> show warnings;
Empty set (0.00 sec)
mysql> update test1 set card_no=card_no +1;
ERROR 1062 (23000): Duplicate entry '1000000001' for key 'test1.uq_card_no'
mysql> update ignore test1 set card_no=card_no +1;
Query OK, 2 rows affected, 1 warning (0.02 sec)
Rows matched: 3 Changed: 2 Warnings: 1
mysql> show warnings;
+---------+------+---------------------------------------------------------+
| Level | Code | Message |
+---------+------+---------------------------------------------------------+
| Warning | 1062 | Duplicate entry '1000000001' for key 'test1.uq_card_no' |
+---------+------+---------------------------------------------------------+
1 row in set (0.00 sec)
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
+----+------------+---------+------+
3 rows in set (0.00 sec)
mysql>
二、忽略非空约束
1、列出字段赋值为null时
当列出需赋值的字段，但是对其中的非空字段赋值为null时，结果如下：
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
+----+------------+---------+------+
3 rows in set (0.00 sec)
mysql> insert into test1(id,card_no,name,c1) values
-> (7,'1000000005',null,'aa');
ERROR 1048 (23000): Column 'name' cannot be null
mysql> insert ignore into test1(id,card_no,name,c1) values (7,'1000000005',null,'aa');
Query OK, 1 row affected, 1 warning (0.01 sec)
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
| 7 | 1000000005 | | aa |
+----+------------+---------+------+
4 rows in set (0.00 sec)
结果为：会插入一个空字符串在表中而不会像正常SQL那样因为非空约束而失败。
有人疑惑，上面是空字符串么，验证结果如下：
mysql> select * from test1 where name='';
+----+------------+------+------+
| id | card_no | name | c1 |
+----+------------+------+------+
| 7 | 1000000005 | | aa |
+----+------------+------+------+
1 row in set (0.00 sec)
mysql> select * from test1 where name is null;
Empty set (0.00 sec)
2、未列出字符串类型字段名
当赋值时未在字段列表中加入有非空约束的字符串类型的字段时，情况如下：
mysql> insert into test1(id,name,c1) values (8,'aaa','aa');
ERROR 1364 (HY000): Field 'card_no' doesn't have a default value
mysql> insert ignore into test1(id,name,c1) values (8,'aaa','aa');
Query OK, 1 row affected, 1 warning (0.01 sec)
mysql> show warnings;
+---------+------+----------------------------------------------+
| Level | Code | Message |
+---------+------+----------------------------------------------+
| Warning | 1364 | Field 'card_no' doesn't have a default value |
+---------+------+----------------------------------------------+
1 row in set (0.00 sec)
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
| 7 | 1000000005 | | aa |
| 8 | | aaa | aa |
+----+------------+---------+------+
5 rows in set (0.01 sec)
可见，字段未列出时，也可以插入成功，也是将其插入一个空字符串。
3、未列整型字段时
当赋值时未在字段列表中加入有非空约束的整型类型的字段时，情况如下：
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
| 7 | 1000000005 | | aa |
| 8 | | aaa | aa |
+----+------------+---------+------+
5 rows in set (0.01 sec)
mysql> insert ignore into test1(card_no,name,c1) values ('1000000006','bbb','aa');
Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> show warnings;
+---------+------+-----------------------------------------+
| Level | Code | Message |
+---------+------+-----------------------------------------+
| Warning | 1364 | Field 'id' doesn't have a default value |
+---------+------+-----------------------------------------+
1 row in set (0.00 sec)
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 0 | 1000000006 | bbb | aa |
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
| 7 | 1000000005 | | aa |
| 8 | | aaa | aa |
+----+------------+---------+------+
6 rows in set (0.00 sec)
mysql>
结果：此时插入了0 （整型的默认值）。
三、字段超长
依旧进行在上述的测试表上进行测试
1、字符串超长
当字符串类型超长时，正常结果如下：
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 0 | 1000000006 | bbb | aa |
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
| 7 | 1000000005 | | aa |
| 8 | | aaa | aa |
+----+------------+---------+------+
6 rows in set (0.00 sec)
mysql> insert into test1(id,card_no,name,c1) values(9,'1000000001','abc','a12345');
ERROR 1406 (22001): Data too long for column 'c1' at row 1
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 0 | 1000000006 | bbb | aa |
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
| 7 | 1000000005 | | aa |
| 8 | | aaa | aa |
+----+------------+---------+------+
6 rows in set (0.00 sec)结果：数据会因超长而未插入。
而使用ignore选项后，结果如下：
mysql> insert ignore into test1(id,card_no,name,c1) values(9,'1000000001','abc','a12345');
Query OK, 1 row affected, 1 warning (0.01 sec)
mysql> show warnings;
+---------+------+-----------------------------------------+
| Level | Code | Message |
+---------+------+-----------------------------------------+
| Warning | 1265 | Data truncated for column 'c1' at row 1 |
+---------+------+-----------------------------------------+
1 row in set (0.00 sec)
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 0 | 1000000006 | bbb | aa |
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
| 7 | 1000000005 | | aa |
| 8 | | aaa | aa |
| 9 | 1000000001 | abc | a1 |
+----+------------+---------+------+
7 rows in set (0.00 sec)
mysql> desc test1;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| card_no | varchar(10) | NO | UNI | NULL | |
| name | varchar(20) | NO | | NULL | |
| c1 | varchar(2) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql>
结果：数据以截断的方式插入成功了。
2、整型数据超长
当普通方式插入一个超过int类型最大值的数据时，会直接因数据超过范围而报错。例如：
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 0 | 1000000006 | bbb | aa |
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
| 7 | 1000000005 | | aa |
| 8 | | aaa | aa |
| 9 | 1000000001 | abc | a1 |
+----+------------+---------+------+
7 rows in set (0.00 sec)
mysql> insert into test1(id,card_no,name,c1) values(999999999999999999999,'1000000003','abc','a2');
ERROR 1264 (22003): Out of range value for column 'id' at row 1
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 0 | 1000000006 | bbb | aa |
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
| 7 | 1000000005 | | aa |
| 8 | | aaa | aa |
| 9 | 1000000001 | abc | a1 |
+----+------------+---------+------+
7 rows in set (0.00 sec)
而使用ignore选项后，可以插入数据，例如：
mysql> select * from test1;
+----+------------+---------+------+
| id | card_no | name | c1 |
+----+------------+---------+------+
| 0 | 1000000006 | bbb | aa |
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
| 7 | 1000000005 | | aa |
| 8 | | aaa | aa |
| 9 | 1000000001 | abc | a1 |
+----+------------+---------+------+
7 rows in set (0.00 sec)
mysql> insert ignore into test1(id,card_no,name,c1) values(999999999999999999999,'1000000003','abc','a2');
Query OK, 1 row affected, 2 warnings (0.01 sec)
mysql> show warnings;
+---------+------+---------------------------------------------+
| Level | Code | Message |
+---------+------+---------------------------------------------+
| Warning | 1264 | Out of range value for column 'id' at row 1 |
| Warning | 1264 | Out of range value for column 'id' at row 1 |
+---------+------+---------------------------------------------+
2 rows in set (0.00 sec)
mysql> select * from test1;
+------------+------------+---------+------+
| id | card_no | name | c1 |
+------------+------------+---------+------+
| 0 | 1000000006 | bbb | aa |
| 1 | 1000000000 | abc | a |
| 3 | 1000000002 | ttt | b |
| 6 | 1000000004 | ccccabc | a |
| 7 | 1000000005 | | aa |
| 8 | | aaa | aa |
| 9 | 1000000001 | abc | a1 |
| 2147483647 | 1000000003 | abc | a2 |
+------------+------------+---------+------+
8 rows in set (0.00 sec)
mysql>
结果： 会以截断的方式插入（int的最大值）
四、结语
总的来说，IGNORE 提供了一种在插入或更新时处理主键、唯一键冲突、非空约束字段未赋值、字段超长等异常时内部自动处理的方法，使得操作不因为某一行的冲突而中断，而是继续处理。但也因为其特点，会导致结果与预期不符的情况。在实际操作中还是建议使用正常的方式进行处理，以免出现不必要的故障。
