How to use ON DUPLICATE KEY for UPDATE

Question

Consider a table of

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

Updating the value of number as

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

or

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

Since external_id-number couple is unique, it will not update if the new value of number exists.

How can I use something like INSERT ... ON DUPLICATE KEY to increase the value of number by number + 1 to reach an available value according to the UNIQUE Constraint and complete the UPDATE task?

Answer 1

First a sample table

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>

Let's insert an initial row and SELECT it back

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>

Let's insert the same thing again

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 let's try the value column at the same time

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>

This time change value and number

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>

Hope this helps.

Give it a Try !!!