#头条创作挑战赛#

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。

1. 主键或唯一键冲突

1.1 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)

1.2 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: 1mysql> 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。

1.3 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: 1mysql> 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。

1.4 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: 1mysql> 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: 1mysql> 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>

2. 忽略非空约束

2.1 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 nullmysql> 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)

2.2 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 valuemysql> 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

2.3 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）。

3. 字段超长

依旧进行在上述的测试表上进行测试

3.1 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 1mysql> 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。

3.2 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 1mysql> 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）

4. 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。

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