MySQL计数查询使用WHERE子句花费的时间太长

Question

I have a MySQL database, and I need to fetch the rows with COUNT.

The database has around 20 million rows, and if I try the following

SELECT COUNT(id) FROM database_rows WHERE database_id = 53;

It takes about 5 minutes for it to fetch the COUNT.

I believe the cause of the issue is the WHERE clause, but I need the where clause to count the rows that I want, not every single row in the table.

SELECT COUNT(id) FROM database_rows;

This query takes about 60ms to run.

I have looked helplessly at online articles, but they provided no sufficient solution.

Is there any way I can optimise this query, and make it take only a few seconds?

Thank you.

Answer 1

An index on the database_id column might help here:

CREATE INDEX idx ON database_rows (database_id);

This assumes that database_id does not already have some sort of index on it and that the value database_id = 53 would be a fairly infrequent occurrence. If either of these criteria be not true, then adding the index might not help.