数据库SQL小技巧大揭秘：IGNORE选项让你的数据处理更从容

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。