Question

For example, I’m doing the next action:

SELECT COUNT(id) 
  FROM users 
 WHERE unique_name = 'Wiliam'

// if Wiliam don't exists then...

INSERT INTO users 
   SET unique_name = 'Wiliam'

The question is, I’m doing the SELECT COUNT(id) check every time I insert a new user, despite of using an unique key or not, so… if “unique_name” has an UNIQUE key it will be better for performance than using a normal key?

Answer 1

What you mean is a UNIQUE CONSTRAINT on the column which will be updated. Reads will be faster, Inserts will be just a bit slower. It will still be faster than your code checking first and then inserting the value though. Just let mysql do its thing and return an error to you if the value is not unique.