mysql - 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 some_condition);

2. SELECT 1 FROM table1 WHERE some_condition LIMIT 0,1;

3. SELECT COUNT(1) FROM table1 WHERE some_condition;

It seems that for MySQL the first approach is more efficient: Best way to test if a row exists in a MySQL table

Is it true in general for any database?

UPDATE:

I've added a third option.

UPDATE2:

Let's assume the database products are mysql, oracle and sql-server.

Answer 1

If you mean to use as a test if AT LEAST ONE row exists with some condition (1 or 0, true or false), then:

select count(1) from my_table where ... and rownum < 2;

Oracle can stop counting after it gets a hit.