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Asked: 2026-05-15T22:36:28+00:00

Right now, I’m debating whether or not to use COUNT(id) or count columns. I

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Right now, I’m debating whether or not to use COUNT(id) or “count” columns. I heard that InnoDB COUNT is very slow without a WHERE clause because it needs to lock the table and do a full index scan. Is that the same behavior when using a WHERE clause?

For example, if I have a table with 1 million records. Doing a COUNT without a WHERE clause will require looking up 1 million records using an index. Will the query become significantly faster if adding a WHERE clause decreases the number of rows that match the criteria from 1 million to 500,000?

Consider the “Badges” page on SO, would adding a column in the badges table called count and incrementing it whenever a user earned that particular badge be faster than doing a SELECT COUNT(id) FROM user_badges WHERE user_id = 111?

Using MyIASM is not an option because I need the features of InnoDB to maintain data integrity.

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  1. Editorial Team

    I wouldn’t say avoid, but it depends on what you are trying to do:

    • If you only need to provide an estimate, you could do SELECT MAX(id) FROM table. This is much cheaper, since it just needs to read the max value in the index.

    • If we consider the badges example you gave, InnoDB only needs to count up the number of badges that user has (assuming an index on user_id). I’d say in most case that’s not going to be more than 10-20, and it’s not much harm at all.

    It really depends on the situation. I probably would keep the count of the number of badges someone has on the main user table as a column (count_badges_awarded) simply because every time an avatar is shown, so is that number. It saves me having to do 2 queries.

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