MySQL多个限制为1的查询会提高UNION的速度吗？

Question

I have 3 queries ending in limit 1 from a database of around 170,000 records.

Is there any difference if I run these 3 queries separately or will combining all 3 by using UNION improve the speed? Currently the query is slow to return the results.

So the end result will return 3 records from the database.

My current queries:

select * from table where cat = '%1%' and brand like '%example%' limit 1;
select * from table where cat = '%2%' and brand like '%example2%' limit 1;
select * from table where cat = '%3%' and brand like '%example3%' limit 1;

With UNION:

(select * from table where cat = '%1%' and brand like '%example%' limit 1) UNION     (select * from table where cat = '%2%' and brand like '%example2%' limit 1) UNION (select *     from table where cat = '%3%' and brand like '%example3%' limit 1);

Answer 1

union will execute all three queries, and then attempt to remove duplicates from them, so it will almost certainly decrease performance. Using union all instead of running three separate queries may slightly improve performance, as it will save the back-and-forth of three independent executions.