Should I COUNT(*) or not?

Question

I know it\'s generally a bad idea to do queries like this:

SELECT * FROM `group_relations`

But when I just want the count, should I go for this

Answer 1

COUNT(*) facts and myths:

MYTH: "InnoDB doesn't handle count(*) queries well":

Most count(*) queries are executed same way by all storage engines if you have a WHERE clause, otherwise you InnoDB will have to perform a full table scan.

FACT: InnoDB doesn't optimize count(*) queries without the where clause

Answer 2

It is best to count by an indexed column such as a primary key.

SELECT COUNT(`group_id`) FROM `group_relations`