Re: index usage for min() vs. "order by asc limit 1"

I don't think you want the group by in that first query.

postgres=# explain analyze select min(id) from delayed_jobs where strand='sis_batch:account:15' group by strand;

                                                      QUERY PLAN

--------------------------------------------------------------------------------------------------------------------------

GroupAggregate  (cost=0.00..8918.59 rows=66 width=29) (actual time=226.759..226.760 rows=1 loops=1)

 ->  Seq Scan on delayed_jobs  (cost=0.00..8553.30 rows=72927 width=29) (actual time=0.014..169.941 rows=72268 loops=1)

       Filter: ((strand)::text = 'sis_batch:account:15'::text)

Total runtime: 226.817 ms

(4 rows)

postgres=# explain analyze select id from delayed_jobs where strand='sis_batch:account:15' order by id limit 1;

                                                                     QUERY PLAN

---------------------------------------------------------------------------------------------------------------------------------------------------------

Limit  (cost=0.00..0.33 rows=1 width=8) (actual time=0.097..0.098 rows=1 loops=1)

 ->  Index Scan using index_delayed_jobs_on_strand on delayed_jobs  (cost=0.00..24181.74 rows=72927 width=8) (actual time=0.095..0.095 rows=1 loops=1)

       Index Cond: ((strand)::text = 'sis_batch:account:15'::text)

Total runtime: 0.129 ms

(4 rows)

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