How to decrement a value in MySQL keeping it above zero?

You can decrement value in MySQL with update command. With this, you can also restrict the value to not reach below 0.

The syntax is as follows −

update yourTableName set yourColumnName = yourColumnName - 1 where yourColumnName > 0;

To avoid the value to go below zero, you can use yourColumnName > 0.

To understand the above syntax, let us create a table. The query to create a table.

mysql> create table DecrementDemo
   −> (
   −> DecrementValue int
   −> );
Query OK, 0 rows affected (0.62 sec)

Insert some records in the table with insert statement. The query is as follows −

mysql> insert into DecrementDemo values(15),(14),(13),(12),(11),(10);
Query OK, 6 rows affected (0.18 sec)
Records: 6 Duplicates: 0 Warnings: 0

Now you can display all records from table with the help of select statement. The query is as follows −

mysql> select *from DecrementDemo;

The following is the output −

+----------------+
| DecrementValue |
+----------------+
|             15 |
|             14 |
|             13 |
|             12 |
|             11 |
|             10 |
+----------------+
6 rows in set (0.00 sec)

Here is the query to decrement value from a table −

mysql> update DecrementDemo
   −> set DecrementValue = DecrementValue - 1 where DecrementValue > 0;
Query OK, 6 rows affected (0.16 sec)
Rows matched: 6 Changed: 6 Warnings: 0

Check whether the value decremented or not using the following query −

mysql> select *from DecrementDemo;

The following is the output −

+----------------+
| DecrementValue |
+----------------+
|             14 |
|             13 |
|             12 |
|             11 |
|             10 |
|              9 |
+----------------+
6 rows in set (0.00 sec)