Why are certain types of prepared queries using PDO in PHP with MySQL slow?

Question

When using SELECT * FROM table WHERE Id IN ( .. ) queries with more than 10000 keys using PDO with prepare()/execute(), the performance degrades ~10X more than

Answer 1

Make sure you're telling PDO that the value is an integer not a string; if PDO puts it as a string, then MySQL will have to typecast the values for comparison. Depending on how it goes about this, it could cause major slowdowns by causing MySQL to avoid using an index.

I'm not completely sure about the behaviour here, but I have had this problem with Postgres a few years back...