Return just the first result of mysql Query

Question

In one of my applications, I have to determine if 'foo_id' is present in the 'foo' column of a table 'foo_table'.

My requirements will be met as soon as I know there is one such 'foo_id' present. Now, my question is how to restrict this to the first match.

When I checked these queries against mySql EXPLAIN:

- select count(foo) from foo_table where foo=<foo_id>;
- select foo from foo_table where foo=<foo_id> limit 1;

In both of the cases, the number of rows was 58. Is there a way in mySql such that I can restrict the number of rows to 1 (the first match), such that rows are not touched unnecessarily (because I don't need that).

Answer 1

You can use EXISTS as such:

SELECT EXISTS(SELECT 1 FROM foo_table WHERE foo=<foo_id>).

The SELECT is ignored as EXISTS only checks the WHERE clause. As it is good practice to avoid using *, it is substituted by 1 here.

Here is the Documentation.

Answer 2

explain plan will always show 58, because is number of records which match you criteria.

However LIMIT 1 is all you need.