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A little background – I have various multi-column
indexes whenever I have queries which restrict the output based on the values
of the 2 fields (for example, a client code and the date of a transaction). Is there a performance gain using this approach as opposed
to using 2 separate indexes, one on the first column and one on the second
column? The reason I am asking is that my coding convetion goes back
to the days where I used ISAM tables, so the systems did not know how to use
more than a single index. In some cases, I may have an index on (columna, columnb) and
one on (columnb, columna) due to the data access patterns. If there are
no performance gains in having these multi-part indexes, and performance will
be the same as having one index solely on columna and one solely on columnb,
then I can reduce the disk usage significantly in some cases. |
