I have two tables with about 25k rows in each, and I am trying to find the differences between the two tables. The query is causing mysql to crash.

This is the query:

Code MySQL:
SELECT *
FROM data
WHERE item NOT IN (
SELECT item
FROM data_backup)

The item column is a varchar, but it contains a 13 digit number only. I am trying to find how many items from my inventory appear in one table over the over.

Oh, I am using MySQL client version: 5.1.49

Any ideas?