At 13:34 -0400 10/9/07, Baron Schwartz wrote:
>Looks like you've found the solution you need. The only other
>suggestion I have is to use UNION ALL if you don't need to eliminate
>duplicate rows in the UNION, because there's some overhead for
>checking for them.
Thanks for this, and I did try it, but the difference in time taken
to execute the query was negligible (I tested it multiple times) - it
was around 0.02 seconds whichever way I did it, and when I used
EXPLAIN, the results were identical except for one detail:
The number of rows in the first row of the EXPLAIN result was lower
with plain UNION than if I used UNION ALL. As far as I can tell from
my relatively limited experience with all this, the first row refers
to my outer 'wrapper' select from the derived table (the table in the
first row is given as '<derived2>' and the Extra column shows 'Using
temporary'). For a given query, with UNION ALL that has 45 rows, with
UNION it's 31. So I guess I'll stick to plain UNION.
As far as my desire to cope with multiple search terms is concerned,
I realise now that fulltext handles that anyway! So I've changed the
few non-numeric fields that weren't indexed that way (fore, sur and
topic) to fulltext and bingo! Not only that, but it all happens fully
FOUR TIMES as quickly!
So many thanks, Baron - mainly due to you, yesterday was a very good
MySQL day for me. It's not often I get two 'lightbulb moments' on the
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