an efficient way to test if a table row exists

Question

I\'m trying to find the most efficient way to determine if a table row exists.

I have in mind 3 options:

1. SELECT EXISTS(SELECT 1 FROM table1 WHERE so

Answer 1

The different methods have different pros and cons:

SELECT EXISTS(SELECT 1 FROM table1 WHERE some_condition);

might be the fastest on MySQL, but

SELECT COUNT(1) FROM table 1 WHERE some_condition

as in @Luis answer gives you the count.

More to the point I recommend you take a look at your business logic: Very seldom is it necessary to just see if a row exists, more often you will want to

• either use these rows, so just do the select and handle the 0-rows case
• or you will want to change these rows, in which case just do your update and check mysql_affected_rows()
• If you want to INSERT a row if it doesn't already exist, take a look at INSERT .. ON DUPLICATE KEY or REPLACE INTO