Thread: Why is UPDATE with column-list syntax not implemented

9.3 documentation says:

According to the standard, the column-list syntax should allow a list of
columns to be assigned from a single row-valued expression, such as a
sub-select:

UPDATE accounts SET (contact_last_name, contact_first_name) =   (SELECT last_name, first_name FROM salesmen    WHERE
salesmen.id= accounts.sales_id); 
This is not currently implemented — the source must be a list of independent
expressions.

Why is this not implemented? Is it considered inconvenient to use, or
difficult to implement. or not important enough, or some other reason?



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AK <alkuzo@gmail.com> writes:
> 9.3 documentation says:
> According to the standard, the column-list syntax should allow a list of
> columns to be assigned from a single row-valued expression, such as a
> sub-select:

> UPDATE accounts SET (contact_last_name, contact_first_name) =
>     (SELECT last_name, first_name FROM salesmen
>      WHERE salesmen.id = accounts.sales_id);
> This is not currently implemented — the source must be a list of independent
> expressions.

> Why is this not implemented? Is it considered inconvenient to use, or
> difficult to implement. or not important enough, or some other reason?

It's difficult to implement.  You'd need to do some significant
restructuring of the way UPDATE is handled.  Probably someone will
attempt it at some point.
        regards, tom lane

Thank you, Tom!



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