Hi RBS,
- indexes that include all possible combinations of fields that may
appear
in a WHERE clause.
As an aside, note that, AFAIK, indexes are only used:
1. To get the first match of a query. If you ask for more than one
matching record, the second, third etc matches are found by searching,
not through the index.
2. From left to right in the same order as your index. So if you
create index MyIndex on MyTable ( Column1, Column2, Column3 ), then
you must test them in the same order, eg: where Column1 = Value1 and
Column2 = Value2 or Column3 = Value3. If you miss a column in the
sequence or place one out of order, the index won't be used from that
point in the test onwards.
3. In equality tests, eg "=" (equals) and "in". If you use "like" for
comparison, the index isn't used. The last test (only) may be one or
two inequality tests, such as ">" or "<". And that last test must be
in sequence (ie rule 2).
I hope this helps a bit. Some more learned SQLiters out there may care
to correct or clarify.
Tom
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