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Rushmore optimization and SELECT DISTINCT
Message
De
11/12/1997 18:15:13
 
 
À
11/12/1997 09:43:25
Information générale
Forum:
Visual FoxPro
Catégorie:
Autre
Divers
Thread ID:
00064798
Message ID:
00065429
Vues:
36
>>>but I my opinion Rushmore SHOULD be about using existing indexes to achieve the fastest query performance possible.
>>
>>
>>>To ignore UNIQUE index tags is a waste and to be able to beat the performance of SQL by an order of magnitude
>>>with old style xbase code is crazy.
>>
>>Do you have deleted records in your table that has UNIQUE indexes?
>>
>>Vlad
>
>Sometimes I have deleted records - other times not. Also, when there might be deleted records, I add the FOR NOT DELETED() to the tag.

Ok, this is correct. I asked you because I was not sure that you're aware that you need the FOR NOT DELETED() clause.

As for the use of UNIQUE indexes in Rushmore optimizations for SELECT-SQL: I see only one very special case when they could be used:

SELECT TagExpr AS AField DISTINCT FROM ATable

where the TagExpr is the expression of the UNIQUE index.

I don't see any other case when they could be used for optimizations. Something similar goes for the indexes with a FOR clause.

Am I right?

Vlad
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