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Which SQL Select would be faster?
Message
Information générale
Forum:
Visual FoxPro
Catégorie:
Base de données, Tables, Vues, Index et syntaxe SQL
Versions des environnements
Visual FoxPro:
VFP 9 SP1
Divers
Thread ID:
01095983
Message ID:
01095995
Vues:
14
Thank you for your input. I did try a few queries but it is hard to tell which is faster with just a few hundred records in my test data. The subquery I had worked too, however. Yours probably work too. Now I am wondering between 3 cases (instead of two). Thanks for your help <g>.

>First, the proof is in the pudding (pardon the metaphor). Try both and see which is better, however, your second query should be as follows:
>
>select * FROM PARENT WHERE PK_fld IN (SELECT distinct PK_FLD FROM CHILD WHERE
>(&cChildFilter))
>
>
>Good Luck.
>
>
>>I need to select records from a Parent Table filtering on fields
>>in the Child Table. But I only need to select (show) fields from the Parent table.
>>
>>I am deciding which approach would be faster:
>>
>>
>>*-- Approach 1. Selecting records from both tables with JOIN and
>>*-- then grouping them
>>select MAX(PARENT.FLD1), MAX(PARENT.FLD2) from PARENT
>>  left join CHILD where (&cChildFilter) GROUP BY PARENT.PK_FLD
>>
>>
>>vs
>>
>>
>>*-- Approach 2. Selecting record from Parent table with subquery
>>*-- from Child table.
>>select P.* FROM PARENT P WHERE EXIST (SELECT * FROM CHILD C WHERE
>>(&cChildFilter) AND C.PK_FLD = P.PK_FLD)
>>
>>
>>I would appreciate any suggestions/input.
"The creative process is nothing but a series of crises." Isaac Bashevis Singer
"My experience is that as soon as people are old enough to know better, they don't know anything at all." Oscar Wilde
"If a nation values anything more than freedom, it will lose its freedom; and the irony of it is that if it is comfort or money that it values more, it will lose that too." W.Somerset Maugham
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