MySQL Query IN() Clause Slow on Indexed Column

Question

I Have a MySQL query that is being generated by a PHP script, the query will look something like this:

SELECT * FROM Recipe_Data WHERE 404_Without_200 = 0 A         


        

Answer 1

The problem is that IN is basically treated as a bunch of ORs (e.g.

col IN (1,2,3)

is

col = 1 OR col = 2 OR col = 3

This is a LOT slower than a join.

What you should do is to generate the SQL code which creates the temporary table, populates it with the values in the "IN" clause, and then join with that temp table

CREATE TEMPORARY TABLE numbers (n INT)

Then in a loop, add

INSERT numbers  VALUES ($next_number)

Then at the end

SELECT * FROM numbers, Recipe_Data 
WHERE numbers.n = RHD_No