On a table with columns a,b,c,d,e,f,g,h,i,j,k I get:
select * from misty order by a limit 25;
Time: 302.068 ms
And:
select c,b,j,k,a,d,i,g,f,e,h from misty order by a limit 25;
Time: 1258.451 ms
Is there a way to make the select by column as fast?
Update:
No index on a table, newly created one
Here is the EXPLAIN ANALYZE, does not seem too helpful:
explain analyze select * from misty order by a limit 25;
Limit (cost=43994.40..43994.46 rows=25 width=190) (actual time=404.958..404.971 rows=25 loops=1)
-> Sort (cost=43994.40..45731.11 rows=694686 width=190) (actual time=404.957..404.963 rows=25 loops=1)
Sort Key: a
Sort Method: top-N heapsort Memory: 28kB
-> Seq Scan on misty (cost=0.00..24390.86 rows=694686 width=190) (actual time=0.013..170.945 rows=694686 loops=1)
Total runtime: 405.019 ms
(6 rows)
And:
explain analyze select c,b,j,k,a,d,i,g,f,e,h from misty order by a limit 25;
Limit (cost=43994.40..43994.46 rows=25 width=190) (actual time=1371.735..1371.745 rows=25 loops=1)
-> Sort (cost=43994.40..45731.11 rows=694686 width=190) (actual time=1371.733..1371.736 rows=25 loops=1)
Sort Key: a
Sort Method: top-N heapsort Memory: 28kB
-> Seq Scan on misty (cost=0.00..24390.86 rows=694686 width=190) (actual time=0.015..516.355 rows=694686 loops=1)
Total runtime: 1371.797 ms
(6 rows)
select *
case and approx 2.2s for the select with columns listed in a different order. – Colin 't Hart May 25 '15 at 9:09select *
. – Colin 't Hart May 25 '15 at 9:11