update a column by subtracting a value

开发者_JAVA技巧

I'm trying to come up with a MySQL query that will update points... Can I do something like this?

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

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UPDATE a75ting.username
SET points = points - 5

by putting the single quotes around the "points -5", you converted that expression into a plaintext string. Leaving it without the quotes lets MySQL see you're referring to a field (points) and subtracting 5 from its current value.

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Run this query to find out the difference:

SELECT '`points` - 5' AS string, `points` - 5 AS expression
FROM a75ting.username