How to Correctly Decrement a Column Value in MySQL?

Modifying a Column by Deducting a Value from a MySQL Database

In the realm of MySQL, you may encounter scenarios where you need to decrement the value of a specific column in a table. To achieve this, you can utilize the UPDATE statement in conjunction with an arithmetic expression.

Query Example

Consider a hypothetical situation where you aim to subtract 5 from the "points" column in the "username" table of the "a75ting" database. You might initially attempt the following query:

UPDATE `a75ting`.`username` SET `points` = '`points` - 5'

Pitfall to Avoid

To your surprise, the query above may not produce the desired result. The reason for this lies in the single quotes surrounding the expression "points - 5". By enclosing the expression in quotes, you essentially converted it into a plaintext string rather than a calculation.

Correct Approach

To correctly decrement the "points" column, you need to remove the single quotes and leave the expression as follows:

UPDATE `a75ting`.`username`
SET `points` = `points` - 5

With this revised query, MySQL will recognize that you are referring to the "points" field and performing a subtraction operation with the value 5. It will then deduct 5 from the existing value in the "points" column for each matching row in the table.

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