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How to subtract by 1 if the field value > 0 in MySQL?
You can use CASE statement with UPDATE command for this. Let us first create a table −
mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, Value int ); Query OK, 0 rows affected (1.44 sec)
Insert records in the table using insert command −
mysql> insert into DemoTable(Value) values(100); Query OK, 1 row affected (0.47 sec) mysql> insert into DemoTable(Value) values(0); Query OK, 1 row affected (4.16 sec) mysql> insert into DemoTable(Value) values(104); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable(Value) values(0); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable(Value) values(5); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable(Value) values(10); Query OK, 1 row affected (0.24 sec) mysql> insert into DemoTable(Value) values(0); Query OK, 1 row affected (0.18 sec)
Display records from the table using select command −
mysql> select *from DemoTable;
This will produce the following output −
+----+-------+ | Id | Value | +----+-------+ | 1 | 100 | | 2 | 0 | | 3 | 104 | | 4 | 0 | | 5 | 5 | | 6 | 10 | | 7 | 0 | +----+-------+ 7 rows in set (0.00 sec)
Now use to set the condition to subtract if the field value is more than 0 if field value > 0, else let it remain the same −
mysql> update DemoTable set Value=CASE WHEN Value > 0 THEN Value-1 ELSE 0 END; Query OK, 4 rows affected (0.25 sec) Rows matched: 7 Changed: 4 Warnings: 0
Let us check table records once again −
mysql> select *from DemoTable;
This will produce the following output −
+----+-------+ | Id | Value | +----+-------+ | 1 | 99 | | 2 | 0 | | 3 | 103 | | 4 | 0 | | 5 | 4 | | 6 | 9 | | 7 | 0 | +----+-------+ 7 rows in set (0.00 sec)
Updated on: 30-Jul-2019
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