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Allow pushdown of HAVING clauses with grouping sets

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In some cases, we may want to transfer a HAVING clause into WHERE in
hopes of eliminating tuples before aggregation instead of after.

Previously, we couldn't do this if there were any nonempty grouping
sets, because we didn't have a way to tell if the HAVING clause
referenced any columns that were nullable by the grouping sets, and
moving such a clause into WHERE could potentially change the results.

Now, with expressions marked nullable by grouping sets with the RT
index of the RTE_GROUP RTE, it is much easier to identify those
clauses that reference any nullable-by-grouping-sets columns: we just
need to check if the RT index of the RTE_GROUP RTE is present in the
clause.  For other HAVING clauses, they can be safely pushed down.

Author: Richard Guo
Discussion: https://postgr.es/m/CAMbWs4-NpzPgtKU=hgnvyn+J-GanxQCjrUi7piNzZ=upiCV=2Q@mail.gmail.com
This commit is contained in:
Richard Guo
2024-10-09 17:19:04 +09:00
parent 828e94c9d2
commit 67a54b9e83
3 changed files with 35 additions and 8 deletions
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5
src/test/regress/sql/groupingsets.sql
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@@ -279,6 +279,11 @@ explain (costs off)
select v.c, (select count(*) from gstest2 group by () having v.c)
from (values (false),(true)) v(c) order by v.c;
-- test pushdown of HAVING clause that does not reference any columns that are nullable by grouping sets
explain (costs off)
select a, b, count(*) from gstest2 group by grouping sets ((a, b), (a)) having a > 1 and b > 1;
select a, b, count(*) from gstest2 group by grouping sets ((a, b), (a)) having a > 1 and b > 1;
-- HAVING with GROUPING queries
select ten, grouping(ten) from onek
group by grouping sets(ten) having grouping(ten) >= 0