User defined variables inside update statement

[Dragos Matei]

Hello,

Has anyone used user-defined session variables to avoid an extra select ?
For e.g. to give away one record from a stockpile, one would run something
like:

UPDATE `promotion_codes`
SET `is_claimed` = 1,
`code` = (@promotion_code := `code`)
WHERE `promotion_type` = 3
LIMIT 1;

SELECT @promotion_code;

This way, the SELECT will be fast since it just reads the value in memory
without going to the table space.

But could there be any issues with using user-defined variables like this,
inside update statements with limit 1 ?

Best,
Dragos