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De
14/05/2021 14:48:22
Walter Meester
HoogkarspelPays-Bas
 
 
À
14/05/2021 14:44:32
Thomas Ganss (En ligne)
Main Trend
Frankfurt, Allemagne
Information générale
Forum:
Visual FoxPro
Catégorie:
Base de données, Tables, Vues, Index et syntaxe SQL
Divers
Thread ID:
01680377
Message ID:
01680468
Vues:
38
>>I'm not claiming to be all knowing, but I don't think there are many people having in depth knowledge of the SQL optimizer in the first place. I've spend almost 3 decades optimizing database access, so yes, I like to think I have at least a reasonable level of understanding of what it does,
>>
>>>2 queries get different query plans. Each plan may have different optimization.
>>
>>Ok, I'll bite here.
>>
>>
SELECT *  FROM sometable
>>and 
>><Pre>SELECT ...full field list ... FROM
>>
>>Will most likely share the same execution plan as
>>1. In both cases the whole table is scanned because there is no WHERE clause
>>2. The same field output is requested
>>
>That was my almost identical 1st thought. Then I began to wonder if this only holds true to "normal", row saving tables or if a columnar data store might introduce differences...

The two points would still stand. When you only select a few fields from the table, it becomes a whole different game.
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