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

On 2023-07-20 15:09:22 +0800, gzh wrote:
> Hi everyone,
>
>
> I'm running into some performance issues with my SQL query.
>
> The following SQL query is taking a long time to execute.
>
>
> explain analyze
> select COUNT(ET_CD)
> from TBL_SHA
> WHERE TBL_SHA.MS_CD = '009'
> and TBL_SHA.ETRYS in
> (select TBL_INF.RY_CD
> from TBL_INF
> WHERE TBL_INF.MS_CD = '009'
> AND TBL_INF.RY_CD = '000001'
> )
>
> ----- Execution Plan -----
[...]
> -> 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 = '009'::bpchar) AND (ETRYS = '000001'::bpchar))
> Rows Removed by Filter: 32000325
[...]
> --------------------------------------------------------------------------------
>
>
> The index is defined as follows.
>
>
> CREATE INDEX index_search_01 ON mdb.TBL_SHA USING btree (MS_CD, ETRYS);
>
>
>
> When I take the following sql statement, the index works fine and the query is
> fast.
>
>
> select COUNT(ET_CD)
> from TBL_SHA
> WHERE MS_CD = '009'
> AND ETRYS = '000001'

What's the plan for that query?

hp

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_ | Peter J. Holzer | Story must make more sense than reality.
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