Re: How to improve the performance of my SQL query？

On Fri, 21 Jul 2023 at 13:44, gzh <gzhcoder(at)126(dot)com> wrote:
>
> The definitions of the columns used in SQL are as follows.
>
> TBL_SHA
> ms_cd character(6) NOT NULL -- PRIMARY KEY
> et_cd character(8)
> etrys character(8)

> explain analyze
> select COUNT(ET_CD)
> from TBL_SHA
> WHERE TBL_SHA.MS_CD = 'MLD009'
> and TBL_SHA.ETRYS in
> (select TBL_INF.RY_CD
> from TBL_INF
> WHERE TBL_INF.MS_CD = 'MLD009'
> AND TBL_INF.RY_CD = '00000001'
> )
> ----- Execution Plan -----
> Limit (cost=2738709.57..2738709.58 rows=1 width=8) (actual time=124168.769..124168.771 rows=1 loops=1)
> -> Aggregate (cost=2738709.57..2738709.58 rows=1 width=8) (actual time=124168.767..124168.769 rows=1 loops=1)
> -> Nested Loop (cost=0.29..2730702.63 rows=3202774 width=9) (actual time=97264.166..123920.769 rows=3200000 loops=1)
> -> Index Only Scan using TBL_INF_pkc on TBL_INF (cost=0.29..8.31 rows=1 width=9) (actual time=0.025..0.030 rows=1 loops=1)
> Index Cond: ((MS_CD = 'MLD009'::bpchar) AND (RY_CD = '00000001'::bpchar))
> Heap Fetches: 1
> -> Seq Scan on TBL_SHA (cost=0.00..2698666.58 rows=3202774 width=18) (actual time=97264.138..123554.792 rows=3200000 loops=1)
> Filter: ((MS_CD = 'MLD009'::bpchar) AND (ETRYS = '00000001'::bpchar))
> Rows Removed by Filter: 32000325
> Planning Time: 0.162 ms
> Execution Time: 124168.838 ms

You might want to check your description of the table definitions.
Going by the above EXPLAIN ANALYZE output, it very much does not look
like ms_cd is the primary key of TBL_SHA. If it is then it's very
weird that you have 3200000 rows for MS_CD = 'MLD009'. You have some
data corruption if that's the case. I suspect you've just not
accurately described the table definition, however.

David