how this query works?

[Saurabh Arora]

Hi

Query 1 - >

Select bla from (
select bla from tablename1 where id='1234' Limit 1
Union
select bla from tablename2 where id='1234' Limit 1
Union
select bla from tablename3 where id='1234' Limit 1
) Limt 1

Q-> how does this query actually executes? Does it stop executing when it finds that 1 row and returns the result immediately???
if not, how should i write a query that gives me 1 row of data i need as soon as it finds it in the tables i am searching.


Query 2-
Select count(*), match(col) against(val) from (
select bla from tablename1 where match(col) against(val) Limit 15
Union
select bla from tablename2 where match(col) against(val) Limit 15
Union
select bla from tablename3 where match(col) against(val) Limit 15
) Limt 15


What does this query exactly do and how does this execute?

Thanks a ton.
Saurabh.


P.S - > comments on optimizing these queries for table rows >50K are most welcome.