Re: [HACKERS] Some progress on INSERT/SELECT/GROUP BY bugs

Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> writes:
> Tom, was this done?

This is not done --- I wasn't willing to try to do such a thing by
myself when we were already in 6.5 beta. It's on my todo list for 6.6.

6.5 fails in a different way than 6.4 did, for reasons that I don't
recall offhand, but the only real fix is to restructure the analyzer.

regards, tom lane

>> I believe I've identified the main cause of the peculiar behavior we
>> are seeing with INSERT ... SELECT ... GROUP/ORDER BY: it's a subtle
>> parser bug.
>>
>> Here is the test case I'm looking at:
>>
>> CREATE TABLE si_tmpverifyaccountbalances (
>> type int4 NOT NULL,
>> memberid int4 NOT NULL,
>> categoriesid int4 NOT NULL,
>> amount numeric);
>>
>> CREATE TABLE invoicelinedetails (
>> invoiceid int4,
>> memberid int4,
>> totshippinghandling numeric,
>> invoicelinesid int4);
>>
>> INSERT INTO si_tmpverifyaccountbalances SELECT invoiceid+3,
>> memberid, 1, totshippinghandling FROM invoicelinedetails
>> GROUP BY invoiceid+3, memberid, totshippinghandling;
>>
>> ERROR: INSERT has more expressions than target columns
>>
>> The reason this is coming out is that the matching of GROUP BY (also
>> ORDER BY) items to targetlist entries is fundamentally broken in this
>> context. The GROUP BY items "memberid" and "totshippinghandling" are
>> simply unvarnished Ident nodes when they arrive at findTargetlistEntry()
>> in parse_clause.c; what findTargetlistEntry() does with them is to try
>> to match them against the resdom names of the existing targetlist items.
>> I think that's correct behavior in the plain SELECT case (but note it
>> means "SELECT a AS b, b AS c GROUP BY b" will really group by a not b
>> --- is that per spec??). But it fails miserably in the INSERT/SELECT
>> case, because by the time control gets here, the targetlist items have
>> been given resdom names *corresponding to the column names of the target
>> table*.
>>
>> So, in the example at hand, "memberid" is matched to the correct column
>> by pure luck (because it has the same name in the destination table),
>> and then "totshippinghandling" is not recognized as one of the existing
>> TLEs because it does not match any destination column name.
>>
>> Now, call me silly, but it seems to me that SELECT ... GROUP BY ought
>> to mean the same thing no matter whether there is an INSERT in front of
>> it or not, and thus that letting target column names affect the meaning
>> of GROUP BY items is dead wrong. (Don't have a spec to check this with,
>> however.)
>>
>> I believe the most reasonable fix for this is to postpone relabeling
>> of the targetlist entries with destination column names until after
>> analysis of the SELECT's subsidiary clauses is complete. In particular,
>> it should *not* be done instantly when each TLE is made, which is what
>> MakeTargetEntryIdent currently does. The TLEs should have the same
>> resnames as in the SELECT case until after subsidiary clause processing
>> is done.
>>
>> (MakeTargetEntryIdent is broken anyway because it tries to associate
>> a destination column with every TLE, even the resjunk ones. The reason
>> we see the quoted error message in this situation is that after
>> findTargetlistEntry fails to detect that totshippinghandling is already
>> a TLE, it calls MakeTargetEntryIdent to make a junk TLE for
>> totshippinghandling, and then MakeTargetEntryIdent tries to find a
>> target column to go with the junk TLE. So the revised code should only
>> assign dest column names to non-junk TLEs.)
>>
>> I'm not really familiar enough with the parser to want to tackle this
>> size of change by myself --- Thomas, do you want to do it? I think it's
>> largely a matter of moving code around, but I'm not sure where is the
>> right place for it...
>>
>> regards, tom lane
>>
>>

> --
> Bruce Momjian | http://www.op.net/~candle
> maillist(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
> + If your life is a hard drive, | 830 Blythe Avenue
> + Christ can be your backup. | Drexel Hill, Pennsylvania 19026