Re: min() vs limit optimization
Posted by:
Apachez
Date: July 02, 2006 08:26PM
Well first of all your two queries will most likely produce different results over time. Or rather, you have nothing in your second query that forces the sql engine to produce the same result.
In the second case the processing will be halted once one matching row has been found (limit optimization) and you have no idea which this row might be (can be something currently in key_buffer for example). To make sure that you will get the same result each time you need for example in the second case an ORDER BY.
Currently it is pure luck that your two queries produces the same answer as they look like today.
What does EXPLAIN SELECT tells you about your two queries?
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