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SQL with two JOINs
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04/02/2023 05:48:51
Lutz Scheffler (En ligne)
Lutz Scheffler Software Ingenieurbüro
Dresden, Allemagne
Information générale
Forum:
Visual FoxPro
Catégorie:
Base de données, Tables, Vues, Index et syntaxe SQL
Divers
Thread ID:
01686104
Message ID:
01686107
Vues:
30
>>Hi,
>>
>>This is a very newbie question, I know.
>>
>>I am trying to understand the SQL Select that Tamar Granor kindly helped me with. It has two JOIN clauses. And THEN, after the second JOIN, there are two ON clauses. I didn't know you can do it. I thought that ON should follow the JOIN immediately.
>>And looks like the first ON belong to the top (first) JOIN and the second ON belongs to the bottom (second) JOIN.
>>
>>My question is, how does SQL Server (or VFP for that matter) knows which ON apply to which JOIN?
>>
>>TIA
>
>For all I know, there is the following syntax:
>
>Syntax one: The ON follows the JOIN, from top to bottom
>
>SELECT * ;
>FROM Cur1 ;                     && - 
> INNER JOIN Cur2 ;              && - First Join	&& -
>  ON Cur1.Field=Cur2.Field ;    && +            && |
> ;                                              && | Second Join (this is: to the result of the first)
> INNER JOIN Cur3 ;                              && -        && -
>  ON Cur2.Field=Cur3.Field                      && +        && | ....
>
>
>Syntax two: The ONs follows the JOINs, inside to outside
>
>SELECT *;
> FROM Cur1;                                         && -
>  INNER JOIN Cur2;              && -                && -
>  INNER JOIN Cur3;              && - First Join     && |
>  ON Cur2.Field=Cur3.Field;     && +                && | Second Join (this is: to the result of the first)
> ON Cur1.Field=Cur2.Field                           && +
>
>
>You are free to mix the styles. It might create a headache, but is it possible.
>
>Update: tab to space

Lutz,

Thank you very much for a clear example explaining my question. The second JOIN syntax was new to me.
But now I see that if there are two JOIN clauses, and the second JOIN syntax is used, the first ON must be applied to the first JOIN.
"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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