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Strange query behavior
Message
De
05/02/1999 15:38:23
 
 
À
03/02/1999 19:57:21
Information générale
Forum:
Visual FoxPro
Catégorie:
Codage, syntaxe et commandes
Divers
Thread ID:
00183700
Message ID:
00184510
Vues:
18
>>If I select a subset of tableA using:
>>
>>select * from tableA where ...
>>
>>subsequent queries with the resulting table are 3-4 times faster than if the iniial subset is done using:
>>
>>select tableA.field1, tableA.field2 ...
>>
>>where the only difference is specifying specific fields vs. the *. I've also tried to place a nofilter on the fast query trying slow it down but it doesn't matter.
>>
>>Thanks,
>>Rock Jensen
>
>These tests are only meaningful if you shut down and restart VFP in between. when running unoptimized queries in VFP, VFP is often smart enough to create and use an index for itself (internally- ie it is not available or visible to you).


Done! I've also run into that several times so I always do my benchmarking that way.
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