Re: [HACKERS] 6.4 Aggregate Bug - Mailing list pgsql-hackers

> While testing  my 6.4 patch to allow functions/expressions to be
> specified in the ORDER/GROUP BY  clause (and not in the target list)  I
> came across a nasty little bug.     A segmentation fault gets thrown
> somewhere in replace_agg_clause() when using aggregates, in combination
> with a function or expression.   (I  am still tracking down the
> offending lines of code.  Sorry, the Linux/GCC environment is still new
> to me.)
>
> I backed out my patch, and discovered  the bug was still present.  The
> bug does not exist in version 6.3.2.  Here is an example:
>
> -- This crashes the backend
>     select upper(a) as x, count(k) from t group by x;
>
> --  This works fine
>     select upper(a) as x, count(a) from t group by x;
>
> Notice how in the first query, (the one that does not work) upper() has
> a different argument than count().  And  in the second query (the one
> that works) upper() has the same argument as count().     When using
> count(*) it will always fail.
Here is my initial analysis of the crash.  It appears the types do not
match.  Not sure why.


---------------------------------------------------------------------------

    POSTGRES backend interactive interface
    $Revision: 1.80 $ $Date: 1998/07/18 18:34:09 $
    > select upper(a) as x, count(xmin) from t group by x;
            StartTransactionCommand() at Sat Aug  1 14:55:16 1998


    Breakpoint 1, match_varid (test_var=0x305010, tlist=0x303750) at
    tlist.c:270
    270             type_var = (Oid) test_var->vartype;
    (gdb)
    (gdb) cont
    Continuing.

    Breakpoint 1, match_varid (test_var=0x305110, tlist=0x303750) at
    tlist.c:270
    270             type_var = (Oid) test_var->vartype;
    (gdb) cont
    Continuing.

    Breakpoint 1, match_varid (test_var=0x3048d0, tlist=0x303ad0) at
    tlist.c:270
    270             type_var = (Oid) test_var->vartype;
    (gdb) l
    265     match_varid(Var *test_var, List *tlist)
    266     {
    267             List       *tl;
    268             Oid                     type_var;
    269
    270             type_var = (Oid) test_var->vartype;
    271
    272             Assert(test_var->varlevelsup == 0);
    273             foreach(tl, tlist)
    274             {
    (gdb) call pprint(test_var)
    { VAR
       :varno 1
       :varattno 3
       :vartype 1043
       :vartypmod -1
       :varlevelsup 0
       :varnoold 1
       :varoattno 3
       }
    (gdb) call pprint(tlist)
    (
       { TARGETENTRY
       :resdom
          { RESDOM
          :resno 1
          :restype 25
          :restypmod -1
          :resname "x"
          :reskey 1
          :reskeyop 740
          :resjunk 0
          }

       :expr
          { VAR
          :varno 1
          :varattno 1
          :vartype 25
          :vartypmod -1
          :varlevelsup 0
          :varnoold -1
          :varoattno 1
          }
       }

       { TARGETENTRY
       :resdom
          { RESDOM
          :resno 2
          :restype 28
          :restypmod -1
          :resname "(null)
          "
          :reskey 0
          :reskeyop 0
          :resjunk 0
          }

       :expr
          { VAR
          :varno 1
          :varattno 2
          :vartype 28
          :vartypmod -1
          :varlevelsup 0
          :varnoold 1
          :varoattno -3
          }
       }
    )

--
Bruce Momjian                          |  830 Blythe Avenue
maillist@candle.pha.pa.us              |  Drexel Hill, Pennsylvania 19026
  +  If your life is a hard drive,     |  (610) 353-9879(w)
  +  Christ can be your backup.        |  (610) 853-3000(h)