index ac42b94ef1072d50a92ad30f0f6a8f32075f3b56..7a73c19314b071f1a2db05ac73d098e1955b1d65 100644 (file)
'abc' || i % 10 AS z,
i AS w
FROM generate_series(1,10000) AS i;
-CREATE INDEX abc ON btg(x,y);
+CREATE INDEX btg_x_y_idx ON btg(x,y);
ANALYZE btg;
-- GROUP BY optimization by reorder columns by frequency
SET enable_hashagg=off;
SET max_parallel_workers_per_gather = 0;
-- Utilize index scan ordering to avoid a Sort operation
EXPLAIN (COSTS OFF) SELECT count(*) FROM btg GROUP BY x,y;
- QUERY PLAN
-----------------------------------------
+ QUERY PLAN
+------------------------------------------------
GroupAggregate
Group Key: x, y
- -> Index Only Scan using abc on btg
+ -> Index Only Scan using btg_x_y_idx on btg
(3 rows)
EXPLAIN (COSTS OFF) SELECT count(*) FROM btg GROUP BY y,x;
- QUERY PLAN
-----------------------------------------
+ QUERY PLAN
+------------------------------------------------
GroupAggregate
Group Key: x, y
- -> Index Only Scan using abc on btg
+ -> Index Only Scan using btg_x_y_idx on btg
(3 rows)
-- Engage incremental sort
explain (COSTS OFF) SELECT x,y FROM btg GROUP BY x,y,z,w;
- QUERY PLAN
------------------------------------------
+ QUERY PLAN
+-------------------------------------------------
Group
Group Key: x, y, z, w
-> Incremental Sort
Sort Key: x, y, z, w
Presorted Key: x, y
- -> Index Scan using abc on btg
+ -> Index Scan using btg_x_y_idx on btg
(6 rows)
explain (COSTS OFF) SELECT x,y FROM btg GROUP BY z,y,w,x;
- QUERY PLAN
------------------------------------------
+ QUERY PLAN
+-------------------------------------------------
Group
Group Key: x, y, z, w
-> Incremental Sort
Sort Key: x, y, z, w
Presorted Key: x, y
- -> Index Scan using abc on btg
+ -> Index Scan using btg_x_y_idx on btg
(6 rows)
explain (COSTS OFF) SELECT x,y FROM btg GROUP BY w,z,x,y;
- QUERY PLAN
------------------------------------------
+ QUERY PLAN
+-------------------------------------------------
Group
Group Key: x, y, w, z
-> Incremental Sort
Sort Key: x, y, w, z
Presorted Key: x, y
- -> Index Scan using abc on btg
+ -> Index Scan using btg_x_y_idx on btg
(6 rows)
explain (COSTS OFF) SELECT x,y FROM btg GROUP BY w,x,z,y;
- QUERY PLAN
------------------------------------------
+ QUERY PLAN
+-------------------------------------------------
Group
Group Key: x, y, w, z
-> Incremental Sort
Sort Key: x, y, w, z
Presorted Key: x, y
- -> Index Scan using abc on btg
+ -> Index Scan using btg_x_y_idx on btg
(6 rows)
-- Subqueries
explain (COSTS OFF) SELECT x,y
FROM (SELECT * FROM btg ORDER BY x,y,w,z) AS q1
GROUP BY (w,x,z,y);
- QUERY PLAN
-----------------------------------------------
+ QUERY PLAN
+-------------------------------------------------
Group
Group Key: btg.x, btg.y, btg.w, btg.z
-> Incremental Sort
Sort Key: btg.x, btg.y, btg.w, btg.z
Presorted Key: btg.x, btg.y
- -> Index Scan using abc on btg
+ -> Index Scan using btg_x_y_idx on btg
(6 rows)
explain (COSTS OFF) SELECT x,y
FROM (SELECT * FROM btg ORDER BY x,y,w,z LIMIT 100) AS q1
GROUP BY (w,x,z,y);
- QUERY PLAN
-----------------------------------------------------
+ QUERY PLAN
+-------------------------------------------------------
Group
Group Key: btg.x, btg.y, btg.w, btg.z
-> Limit
-> Incremental Sort
Sort Key: btg.x, btg.y, btg.w, btg.z
Presorted Key: btg.x, btg.y
- -> Index Scan using abc on btg
+ -> Index Scan using btg_x_y_idx on btg
(7 rows)
-- Should work with and without GROUP-BY optimization
@@ -2844,8 +2844,8 @@ explain (COSTS OFF) SELECT x,y FROM btg GROUP BY w,x,z,y ORDER BY y,x,z,w;
-- Utilize incremental sort to make the ORDER BY rule a bit cheaper
explain (COSTS OFF) SELECT x,w FROM btg GROUP BY w,x,y,z ORDER BY x*x,z;
- QUERY PLAN
------------------------------------------------
+ QUERY PLAN
+-------------------------------------------------------
Sort
Sort Key: ((x * x)), z
-> Group
@@ -2853,7 +2853,7 @@ explain (COSTS OFF) SELECT x,w FROM btg GROUP BY w,x,y,z ORDER BY x*x,z;
-> Incremental Sort
Sort Key: x, y, w, z
Presorted Key: x, y
- -> Index Scan using abc on btg
+ -> Index Scan using btg_x_y_idx on btg
(8 rows)
SET enable_incremental_sort = off;