On Thu, 2023-07-20 at 15:09 +0800, gzh wrote:
> 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 -----
> 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..0.030rows=1 loops=1)
> Index Cond: ((MS_CD = '009'::bpchar) AND (RY_CD = '000001'::bpchar))
> Heap Fetches: 1
> -> Seq Scan on TBL_SHA (cost=0.00..2698666.58 rows=3202774 width=18) (actual
time=97264.138..123554.792rows=3200000 loops=1)
> Filter: ((MS_CD = '009'::bpchar) AND (ETRYS = '000001'::bpchar))
> Rows Removed by Filter: 32000325
> Planning Time: 0.162 ms
> Execution Time: 124168.838 ms
> --------------------------------------------------------------------------------
>
> The index is defined as follows.
>
> CREATE INDEX index_search_01 ON mdb.TBL_SHA USING btree (MS_CD, ETRYS);
Actual rows = 3200000, rows removed by filter is ten times as much.
It should use an index.
> 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'
>
> The amount of data in the table is as follows.
> TBL_SHA 38700325
> TBL_INF 35546
This looks very much like it is a problem with the data types.
I see that you are using "character", which you shouldn't do.
What I cannot see is if the columns are defined as "character" or whether you bind
the parameters as "character". Can you show us the table definition of "TBL_SHA"
and "TBL_INF"?
Yours,
Laurenz Albe
