Do a query only if there are no results on previous query

I do this query(1):

(1)SELECT * FROM t1 WHERE title LIKE 'key%' LIMIT 1

I need to do a second(2) query only if this previous query has no results

(2)SELECT * FROM t1 WHERE title LIKE '%key%' LIMIT 1

basically i need only 1 row who got the most close title to my key.

Atm i am using an UNION query with a custom field to order开发者_开发问答 it and a LIMIT 1. Problem is I don't want to do the others query if already the first made the result.

Thanks

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There isn't a standard way to say 'execute query Q2 if and only if query Q1 returns nothing' in a single SQL statement.

The moderately close approach would be:

SELECT * FROM t1 WHERE title LIKE 'key%' LIMIT 1
UNION
SELECT * FROM t1 WHERE title LIKE '%key%'
   AND NOT EXISTS (SELECT * FROM t1 WHERE title LIKE 'key%')
 LIMIT 1

The issue is whether the optimizer would be intelligent enough to realize that the NOT EXISTS sub-query is the first half of the UNION.