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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