Hi again Ed,
SELECT file WITH PRINT.DATE GT "01/04/2008" AND WITH ADDR LIKE "'A'0X"
This query can be resolved with an index. Also, the optimiser will shuffle
the clauses to make best use of indices. Unidata had query optimisation
before UniVerse but I believe that essentially the same algorithms were
ported across for UV 10. I have played games trying to defeat the UV
optimiser and I have to say the I am very impressed by it.
SELECT file WITH PRINT.DATE GT "01/04/2008" OR WITH ADDR LIKE "'A'0X"
This cannot be resolved with an index because the second condition cannot be
determined without reading all the records.
Also, my indexes look to be out of date, as the non-indexed and
indexed selects return different numbers.
That is worrying since the index system is supposed to guarantee consistency
between the data file and the index. The only time that they should ever be
able to get out of step is after a system failure or killing a process in
the middle of a write.
Martin Phillips
Ladybridge Systems Ltd
17b Coldstream Lane, Hardingstone, Northampton, NN4 6DB
+44-(0)1604-709200
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