| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, David Fetter <david(at)fetter(dot)org>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: LATERAL |
| Date: | 2009-10-18 01:08:27 |
| Message-ID: | 27580.1255828107@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Another thought, only semi-related. One of the big use cases for
> LATERAL in general is to use a set-returning function in the FROM
> clause that uses vars from a preceding FROM item. I am idly wondering
> if there's a reason why ExecProject is not its own node type.
You generally need it everywhere. Scan nodes need it because you don't
want unused columns propagating upwards, and join nodes need it because
the two input tuples have to be unified somehow. We do skip projection
ability in a few node types, but I doubt it would be profitable to
remove it from the rest.
regards, tom lane
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