Skip to content

Instantly share code, notes, and snippets.

@kevlarr

kevlarr/README.md

Last active Nov 13, 2019
Embed
What would you like to do?
SQL-y things
/* ***************************************************
Using HAVING to filter by aggregate function results
means not having to select and filter from a subquery.
I wasn't sure if repeating the agg function would
re-run it, so I built a large temporary table and
timed queries with and without the HAVING.
TL;DR:
`SELECT agg(..) FROM .. GROUP BY .. HAVING agg(..)`
~~ does not~~ repeat the aggregate function call,
so this is a pretty awesome trick!
*************************************************** */
/*
Create a temporary table and join several times
to create a large, uneven data set:
i1 | i2 | i3
----+----+----
1 | 1 | 1
2 | 1 | 1
2 | 2 | 1
2 | 2 | 2
3 | 1 | 1
3 | 2 | 1
3 | 2 | 2
3 | 3 | 1
3 | 3 | 2
3 | 3 | 3
4 | 1 | 1
...
10 | 10 | 8
10 | 10 | 9
10 | 10 | 10
(220 rows)
*/
with t as (select generate_series(1, 10) as i)
select t1.i as i1, t2.i as i2, t3.i as i3
from t t1
join t as t2 on t2.i <= t1.i
join t as t3 on t3.i <= t2.i
order by t1.i, t2.i, t3.i
;
-- Up the size and do a GROUP BY w/o aggregate functions
-- to use as the "base" measurement
explain analyze
with t as (select generate_series(1, 500) as i)
select t1.i as i1
from t t1
join t as t2 on t2.i <= t1.i
join t as t3 on t3.i <= t2.i
group by t1.i
order by t1.i
;
/*
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------
Sort (cost=6604170.49..6604170.99 rows=200 width=4) (actual time=30567.533..30567.574 rows=500 loops=1)
Sort Key: t1.i
Sort Method: quicksort Memory: 48kB
CTE t
-> ProjectSet (cost=0.00..5.02 rows=1000 width=4) (actual time=0.015..0.348 rows=500 loops=1)
-> Result (cost=0.00..0.01 rows=1 width=0) (actual time=0.007..0.007 rows=1 loops=1)
-> HashAggregate (cost=6604155.83..6604157.83 rows=200 width=4) (actual time=30567.197..30567.320 rows=500 loops=1)
Group Key: t1.i
-> Nested Loop (cost=0.00..6326378.33 rows=111111000 width=4) (actual time=0.065..23867.591 rows=20958500 loops=1)
Join Filter: (t3.i <= t2.i)
Rows Removed by Join Filter: 41666500
-> CTE Scan on t t3 (cost=0.00..20.00 rows=1000 width=4) (actual time=0.029..0.567 rows=500 loops=1)
-> Materialize (cost=0.00..25499.67 rows=333333 width=8) (actual time=0.006..23.979 rows=125250 loops=500)
-> Nested Loop (cost=0.00..22530.00 rows=333333 width=8) (actual time=0.022..110.981 rows=125250 loops=1)
Join Filter: (t2.i <= t1.i)
Rows Removed by Join Filter: 124750
-> CTE Scan on t t1 (cost=0.00..20.00 rows=1000 width=4) (actual time=0.007..0.157 rows=500 loops=1)
-> CTE Scan on t t2 (cost=0.00..20.00 rows=1000 width=4) (actual time=0.000..0.100 rows=500 loops=500)
Planning Time: 0.285 ms
Execution Time: 30568.055 ms
*/
-- Add `sum` aggregations
explain analyze
with t as (select generate_series(1, 500) as i)
select t1.i as i1, sum(t2.i) as i2_sum, sum(t3.i) as i3_sum
from t t1
join t as t2 on t2.i <= t1.i
join t as t3 on t3.i <= t2.i
group by t1.i
order by t1.i
;
/*
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------
Sort (cost=7159725.49..7159725.99 rows=200 width=20) (actual time=31786.370..31786.411 rows=500 loops=1)
Sort Key: t1.i
Sort Method: quicksort Memory: 64kB
CTE t
-> ProjectSet (cost=0.00..5.02 rows=1000 width=4) (actual time=0.004..0.209 rows=500 loops=1)
-> Result (cost=0.00..0.01 rows=1 width=0) (actual time=0.001..0.002 rows=1 loops=1)
-> HashAggregate (cost=7159710.83..7159712.83 rows=200 width=20) (actual time=31785.967..31786.132 rows=500 loops=1)
Group Key: t1.i
-> Nested Loop (cost=0.00..6326378.33 rows=111111000 width=12) (actual time=0.019..23993.921 rows=20958500 loops=1)
Join Filter: (t3.i <= t2.i)
Rows Removed by Join Filter: 41666500
-> CTE Scan on t t3 (cost=0.00..20.00 rows=1000 width=4) (actual time=0.008..0.526 rows=500 loops=1)
-> Materialize (cost=0.00..25499.67 rows=333333 width=8) (actual time=0.006..23.715 rows=125250 loops=500)
-> Nested Loop (cost=0.00..22530.00 rows=333333 width=8) (actual time=0.006..100.399 rows=125250 loops=1)
Join Filter: (t2.i <= t1.i)
Rows Removed by Join Filter: 124750
-> CTE Scan on t t1 (cost=0.00..20.00 rows=1000 width=4) (actual time=0.001..0.115 rows=500 loops=1)
-> CTE Scan on t t2 (cost=0.00..20.00 rows=1000 width=4) (actual time=0.000..0.090 rows=500 loops=500)
Planning Time: 0.169 ms
Execution Time: 31786.840 ms
*/
-- Add `HAVING` clauses for sums
explain analyze
with t as (select generate_series(1, 500) as i)
select t1.i as i1, sum(t2.i) as i2_sum, sum(t3.i) as i3_sum
from t t1
join t as t2 on t2.i <= t1.i
join t as t3 on t3.i <= t2.i
group by t1.i
having sum(t2.i) > 40000 and sum(t3.i) > 30000
order by t1.i
;
/*
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------
Sort (cost=7715274.34..7715274.40 rows=22 width=20) (actual time=32677.428..32677.465 rows=445 loops=1)
Sort Key: t1.i
Sort Method: quicksort Memory: 59kB
CTE t
-> ProjectSet (cost=0.00..5.02 rows=1000 width=4) (actual time=0.004..0.174 rows=500 loops=1)
-> Result (cost=0.00..0.01 rows=1 width=0) (actual time=0.002..0.002 rows=1 loops=1)
-> HashAggregate (cost=7715265.83..7715268.83 rows=22 width=20) (actual time=32677.017..32677.203 rows=445 loops=1)
Group Key: t1.i
Filter: ((sum(t2.i) > 40000) AND (sum(t3.i) > 30000))
Rows Removed by Filter: 55
-> Nested Loop (cost=0.00..6326378.33 rows=111111000 width=12) (actual time=0.018..24711.548 rows=20958500 loops=1)
Join Filter: (t3.i <= t2.i)
Rows Removed by Join Filter: 41666500
-> CTE Scan on t t3 (cost=0.00..20.00 rows=1000 width=4) (actual time=0.008..0.592 rows=500 loops=1)
-> Materialize (cost=0.00..25499.67 rows=333333 width=8) (actual time=0.006..24.599 rows=125250 loops=500)
-> Nested Loop (cost=0.00..22530.00 rows=333333 width=8) (actual time=0.005..98.609 rows=125250 loops=1)
Join Filter: (t2.i <= t1.i)
Rows Removed by Join Filter: 124750
-> CTE Scan on t t1 (cost=0.00..20.00 rows=1000 width=4) (actual time=0.001..0.106 rows=500 loops=1)
-> CTE Scan on t t2 (cost=0.00..20.00 rows=1000 width=4) (actual time=0.000..0.087 rows=500 loops=500)
Planning Time: 0.220 ms
Execution Time: 32679.939 ms
*/
/*
CONCLUSION:
Including a `HAVING` clause did not appear to re-run any aggregations
(as one would hope), as the timing differences appeared during the
`MATERIALIZE` phase prior to any filters.
*/
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment