Question

I need to select certain rows from a mysql table that has VARCHAR Primary Key index ID.

I therefore use a query (but obviously 13,000 ids instead of 3)

SELECT * FROM table1 WHERE ID IN ('id1928383','id3838339','id38383')

For the majority of tables this works well (~0.2s) but for some tables the query takes much longer (~10-11s).

The only thing different about the tables that do not work is they have a larger Data_length? Any ideas how I can speed up the slow query’s?

Answer 1

There are a few things you can do to speed up this query:

• Use INT instead of VARCHAR for the ID column

Computers in general are much better with numbers than with strings, so this will speed it up considerably.

• Add the ID as an index.

This will create an ordered table with that indexed column, where the searching and ordering will be a LOT faster.

• Use PDO

If you are using this with PHP, I recommend you use PDO, since it has a query caching system, and can significantly improve results if there are many identical queries being run. I suppose other programming languages have similar mechanisms.

• Upgrade MySQL

For all the software you use it is recommended to use the latest version for many reasons. If I’m not mistaking, there was a performance issue with IN in an older version of MySQL, which was fixed a few version later, but you could be one of the unlucky few that still uses that version.

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That’s about as much as I can help, if you need more help, you will need to post more info (table structure, database structure, programming language, etc).