如何使用 ON DUPLICATE KEY 进行更新

Question

考虑一个表

CREATE TABLE test
(
id int(11) unsigned NOT NULL AUTO_INCREMENT,
external_id int(11),
number smallint(5),
value varchar(255),
UNIQUE INDEX (external_id, number),
PRIMARY KEY(id)
) ENGINE=InnoDB

将 number 的值更新为

UPDATE test SET number=number + 1 WHERE external_id='X'

或者

UPDATE test SET number='Y' WHERE external_id='X'

由于 external_id-number 对是唯一的，如果 number 的新值存在，则不会更新。

如何根据 UNIQUE 约束使用类似INSERT ... ON DUPLICATE KEY增加numberby的值number + 1以达到可用值并完成UPDATE任务？

Answer 1

首先是一个示例表

mysql> drop database if exists ali;
Query OK, 1 row affected (0.10 sec)

mysql> create database ali;
Query OK, 1 row affected (0.00 sec)

mysql> use ali;
Database changed
mysql> CREATE TABLE test
    -> (
    -> id int(11) unsigned NOT NULL AUTO_INCREMENT,
    -> external_id int(11),
    -> number smallint(5),
    -> value varchar(255),
    -> UNIQUE INDEX (external_id, number),
    -> PRIMARY KEY(id)
    -> ) ENGINE=InnoDB;
Query OK, 0 rows affected (0.09 sec)

mysql>

让我们插入一个初始行并将其 SELECT 回来

mysql> INSERT INTO test (external_id,number,value)
    -> VALUES (200,15,'Y')
    -> ON DUPLICATE KEY UPDATE number = number + 1;SELECT * FROM test;
Query OK, 1 row affected (0.06 sec)

+----+-------------+--------+-------+
| id | external_id | number | value |
+----+-------------+--------+-------+
|  1 |         200 |     15 | Y     |
+----+-------------+--------+-------+
1 row in set (0.00 sec)

mysql>

让我们再次插入相同的东西

mysql> INSERT INTO test (external_id,number,value)
    -> VALUES (200,15,'Y')
    -> ON DUPLICATE KEY UPDATE number = number + 1;SELECT * FROM test;
Query OK, 2 rows affected (0.10 sec)

+----+-------------+--------+-------+
| id | external_id | number | value |
+----+-------------+--------+-------+
|  1 |         200 |     16 | Y     |
+----+-------------+--------+-------+
1 row in set (0.00 sec)

mysql>

OK 我们同时试试value列

mysql> INSERT INTO test (external_id,number,value)
    -> VALUES (201,15,'X')
    -> ON DUPLICATE KEY UPDATE
    -> number = number + 1,value = VALUES(value);
Query OK, 1 row affected (0.07 sec)

mysql> SELECT * FROM test;
+----+-------------+--------+-------+
| id | external_id | number | value |
+----+-------------+--------+-------+
|  1 |         200 |     16 | Y     |
|  5 |         201 |     15 | X     |
+----+-------------+--------+-------+
2 rows in set (0.00 sec)

mysql> INSERT INTO test (external_id,number,value)
    -> VALUES (201,15,'X')
    -> ON DUPLICATE KEY UPDATE
    -> number = number + 1,value = VALUES(value);
Query OK, 2 rows affected (0.06 sec)

mysql> SELECT * FROM test;
+----+-------------+--------+-------+
| id | external_id | number | value |
+----+-------------+--------+-------+
|  1 |         200 |     16 | Y     |
|  5 |         201 |     16 | X     |
+----+-------------+--------+-------+
2 rows in set (0.00 sec)

mysql>

这次改变值和数字

mysql> INSERT INTO test (external_id,number,value)
    -> VALUES (202,15,'Z')
    -> ON DUPLICATE KEY UPDATE
    -> number = number + 1,
    -> value = VALUES(value);
Query OK, 1 row affected (0.07 sec)

mysql> SELECT * FROM test;
+----+-------------+--------+-------+
| id | external_id | number | value |
+----+-------------+--------+-------+
|  1 |         200 |     16 | Y     |
|  5 |         201 |     16 | X     |
|  8 |         202 |     15 | Z     |
+----+-------------+--------+-------+
3 rows in set (0.00 sec)

mysql> INSERT INTO test (external_id,number,value)
    -> VALUES (202,15,'A')
    -> ON DUPLICATE KEY UPDATE
    -> number = number + 1,
    -> value = VALUES(value);
Query OK, 2 rows affected (0.07 sec)

mysql> SELECT * FROM test;
+----+-------------+--------+-------+
| id | external_id | number | value |
+----+-------------+--------+-------+
|  1 |         200 |     16 | Y     |
|  5 |         201 |     16 | X     |
|  8 |         202 |     16 | A     |
+----+-------------+--------+-------+
3 rows in set (0.00 sec)

mysql>

希望这可以帮助。

试一试 ！！！