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Tweak sorting so that nulls appear at the front of a descending sort

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(vs. at the end of a normal sort).  This ensures that explicit sorts
yield the same ordering as a btree index scan.  To be really sure that
that equivalence holds, we use the btree entries in pg_amop to decide
whether we are looking at a '<' or '>' operator.  For a sort operator
that has no btree association, we put the nulls at the front if the
operator is named '>' ... pretty grotty, but it does the right thing in
simple ASC and DESC cases, and at least there's no possibility of getting
a different answer depending on the plan type chosen.
This commit is contained in:
Tom Lane
2001-06-02 19:01:53 +00:00
parent e542036461
commit 5433b48380
3 changed files with 144 additions and 127 deletions
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27
src/backend/commands/analyze.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/commands/analyze.c,v 1.17 2001/05/07 00:43:17 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/commands/analyze.c,v 1.18 2001/06/02 19:01:53 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -1439,27 +1439,12 @@ compare_scalars(const void *a, const void *b)
int ta = ((ScalarItem *) a)->tupno;
Datum db = ((ScalarItem *) b)->value;
int tb = ((ScalarItem *) b)->tupno;
int32 compare;
if (datumCmpFnKind == SORTFUNC_LT)
{
if (DatumGetBool(FunctionCall2(datumCmpFn, da, db)))
return -1; /* a < b */
if (DatumGetBool(FunctionCall2(datumCmpFn, db, da)))
return 1; /* a > b */
}
else
{
/* sort function is CMP or REVCMP */
int32 compare;
compare = DatumGetInt32(FunctionCall2(datumCmpFn, da, db));
if (compare != 0)
{
if (datumCmpFnKind == SORTFUNC_REVCMP)
compare = -compare;
return compare;
}
}
compare = ApplySortFunction(datumCmpFn, datumCmpFnKind,
da, false, db, false);
if (compare != 0)
return compare;
/*
* The two datums are equal, so update datumCmpTupnoLink[].