Re: How to improve the performance of my SQL query？ - Mailing list pgsql-general

>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"?
For information security reasons, I can't provide the table definition, these columns are defined as "character".

At 2023-07-20 19:58:59, "Laurenz Albe" <laurenz.albe@cybertec.at> wrote:
>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..0.030 rows=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..123554.792 rows=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