Re: Changed SRF in targetlist handling

On 06/06/16 18:30, David G. Johnston wrote:
> To clarify, the present behavior is basically a combination of both of
> Robert's results.
> 
> If the SRFs return the same number of rows the first (zippered) result
> is returned without an NULL padding.
> 
> If the SRFs return a different number of rows the LCM behavior kicks in
> and you get Robert's second result.

No.

> SELECT generate_series(1, 4), generate_series(1, 4) ORDER BY 1, 2;
> is the same as
> SELECT * FROM ROWS FROM ( generate_series(1, 4), generate_series(1, 4) );
> 
> BUT
> 
> ​SELECT generate_series(1, 3), generate_series(1, 4) ORDER BY 1, 2;
> is the same as
> SELECT * FROM ROWS FROM generate_series(1, 3) a, LATERAL ROWS FROM
> generate_series(1, 4) b;

What would you do with:

SELECT generate_series(1, 3), generate_series(1, 6);

?

> Tom's 2.5 proposal basically says we make the former equivalence succeed
> and have the later one fail.
> 
> The rewrite would be unaware of the cardinality of the SRF and so it
> cannot conditionally rewrite the query.  One of the two must be chosen
> and the incompatible behavior turned into an error.


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Vik Fearing                                          +33 6 46 75 15 36
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