From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> |
Cc: | Johannes <jotpe(at)posteo(dot)de>, pgsql-general <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: update inside function does not use the index |
Date: | 2015-11-16 17:19:30 |
Message-ID: | 17585.1447694370@sss.pgh.pa.us |
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Lists: | pgsql-general |
Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> writes:
> On 11/16/2015 08:03 AM, Johannes wrote:
>>> In every loop I execute an update with a where LIKE condition, which
>>> relates to my current cursor position:
>>> FOR i IN SELECT id, level_ids, path_names||'%' as path_names from x LOOP
>>> update x set path_ids[i.level] = id where path_names like i.path_names;
Probably the problem is that the planner is unable to fold i.path_names
to a constant, so it can't derive an indexscan condition from the LIKE
clause.
A little bit of experimentation says that that will work if "i" is
declared with a named rowtype, but not if it's declared RECORD. This
might or might not be something we could fix, but in the meantime I'd
try
DECLARE i x%rowtype;
FOR i IN SELECT * FROM x LOOP
update x set path_ids[i.level] = id where path_names like (i.path_names || '%');
which while it might look less "constant" is actually more so from the
planner's perspective, because there is no question of whether "i" has
got a field of that name.
regards, tom lane
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