Re: NOT IN for Multuple Values

[Rick James]

That's an awfully inefficient way to perform the query.

Instead of

FROM x
WHERE CONCAT(a,b) NOT IN ( SELECT CONCAT(a,b) FROM z ... )

do

FROM x
LEFT JOIN z ON z.a = x.a AND z.b = x.b
WHERE z.id IS NULL

Also don't CONCAT like that in the WHERE clause, it eliminates the possibility of using an index.

WHERE CONCAT(a,'-',b) = 'P-7943'

-->

WHERE a = 'P' AND b = '7943'

and then have INDEX(a,b) (in any order)