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How to optimize SQL query with multiple selects


By : fatchops
Date : October 18 2020, 08:10 AM
hope this fix your issue I have a query that uses multiple SELECTS, and I need to optimize this but I have no clue how to do this. , It is better to write this query using window functions:
code :
select e.* 
from (select last_name, department_id, salary, 
             avg(salary) over (partition by department_id) as avgsalary
      from employees e
     ) e
where salary < avgsalary;


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optimize this query that selects rows before and after a pk


By : user3265135
Date : March 29 2020, 07:55 AM
it fixes the issue Get the rows with an ID less/greater than yours, and limit it to 2 rows.
code :
next_objs = Media.objects.filter(id__gt=image.id).order_by('id')[:2]
prev_objs = Media.objects.filter(id__lt=image.id).order_by('-id')[:2]

Optimize a bunch of nested SELECTs in a MS ACCESS query


By : Aviv
Date : March 29 2020, 07:55 AM
may help you . This is a MS Access query that runs very slow. The Results table is the main table and the P, B, S and C tables are child tables. The column combination Index and ResultID is unique in all of these tables. So for instance, there can only be one row in the table C where Index is "1" and ResultID is 2. I'm not using JOIN because MS Access only support inner joins and what I'd need is an outer join because I want to show all records in the table Results even if there is no corresponding record in any other table. , I am not sure where you got the following:
code :
SELECT 
    [Results].[Id],
    [Results].[Name],
    [Results].[OfferPrice],
    [Results].[RegPrice],
    [Results].[ImageFileName],
    [Results].[Image],
    [Results].[URL],
    max(IIF(P.Index = "0", P.P, null)) as P0,
    max(IIF(P.Index = "1", P.P, null)) as P1,
    max(IIF(P.Index = "2", P.P, null)) as P2,
    max(IIF(P.Index = "3", P.P, null)) as P3,
    max(IIF(P.Index = "4", P.P, null)) as P4,
    max(IIF(P.Index = "5", P.P, null)) as P5,
    max(IIF(B.Index = "0", B.B, null)) as B0,
    max(IIF(B.Index = "1", B.B, null)) as B1,
    max(IIF(B.Index = "8", B.B, null)) as B8,
    max(IIF(S.Index = "2", S.S, null)) as S2,
    max(IIF(C.Index = "1", C.C, null)) as C1
FROM Results
LEFT JOIN P
    on P.ResultID = Results.Id
LEFT JOIN B
    on B.ResultID = Results.Id
LEFT JOIN S
    on S.ResultID = Results.Id
LEFT JOIN C
    on C.ResultID = Results.Id
GROUP BY [Results].[Id],
    [Results].[Name],
    [Results].[OfferPrice],
    [Results].[RegPrice],
    [Results].[ImageFileName],
    [Results].[Image],
    [Results].[URL]
TRANSFORM Max(Src.Value)
select 
    [Results].[Id],
    [Results].[Name],
    [Results].[OfferPrice],
    [Results].[RegPrice],
    [Results].[ImageFileName],
    [Results].[Image],
    [Results].[URL]
from results as R
left join
(
    select ResultID, P as Value, "P"&Index as col
    from p
    union all
    select ResultID, B as Value, "B"&Index as col
    from B
    union all
    select ResultID, C as Value, "C"&Index as col
    from C
    union all
    select ResultID, S as Value, "S"&Index as col
    from S
) as Src
    on R.id = Src.ResultID
GROUP BY [Results].[Id], [Results].[Name],
    [Results].[OfferPrice],[Results].[RegPrice],
    [Results].[ImageFileName], [Results].[Image],
    [Results].[URL]
PIVOT Src.col

How to optimize SQL query with multiple SELECTs from the same table?


By : railsdeveloper1990
Date : March 29 2020, 07:55 AM
I hope this helps . When you want to do a pivot in MySQL you can do Aggregate on a Case statement
code :
SELECT 
    SUM ( CASE WHEN other_same_field  = 0 THEN same_field ELSE 0 END) as A,
    SUM ( CASE WHEN other_same_field  = 1 THEN same_field ELSE 0 END) as B,
    SUM ( CASE WHEN other_same_field  = 2 THEN same_field ELSE 0 END) as C
FROM same_table
WHERE other_same_field IN (0, 1, 2)

Optimize Oracle query with joins and multiple selects


By : Vanneste Koen
Date : March 29 2020, 07:55 AM
this one helps. You should have indices on (Run.rn_test_config_id, Run.rn_run_id) AND (Run.rn_run_id), which should help with the partitioning and subsequent join.
I'd also probably see if tweaking your query like this would help:
code :
SELECT  Test.ts_user_11 AS "Team", 
        Test.ts_test_id AS "Test ID",
        Test.ts_name AS "Test Name",
        TEST.ts_user_06 AS "Priority",
        CASE WHEN Run.rn_status = 'Failed' OR Run.rn_status = 'Issue Found' 
                  THEN 'Ran with Issues'
             WHEN Run.rn_status = 'No Run' AND Run.rn_execution_date IS NOT NULL 
                  THEN 'Skipped'
             WHEN (Run.rn_status = 'No Run' OR Run.rn_status = 'N/A') AND Run.rn_execution_date IS NULL 
                  THEN 'Not Run'
             ELSE Run.rn_status END AS "Exec Status",
        Test.ts_user_03 AS "Type",
        TO_CHAR(Run.rn_execution_date, 'YYYY-MM-DD') AS "Execution Date",
        Run.rn_user_01 AS "Build Number"  
FROM Data_Protection_Hendrix_DB.Run Run
-- one of the few times you can exclude the grouping condition from the results!
-- Only since rn_run_id is distinct
JOIN (SELECT MAX(rn_run_id) AS run_id
      FROM Data_Protection_Hendrix_DB.Run
      GROUP BY rn_test_config_id) Latest_Run
  ON Latest_Run.run_id = Run.rn_run_id
-- kept these as a LEFT JOIN, since that's more likely the intent.
-- I'm not sure that's what you were _getting_, though.
LEFT JOIN Data_Protection_Hendrix_DB.Test
       ON Test.ts_test_id = Run.rn_test_id
          AND Test.ts_template = 'N'
LEFT JOIN Data_Protection_Hendrix_DB.All_Lists
       ON All_Lists.al_item_id = Test.ts_subject
          AND All_Lists.al_absolute_path NOT LIKE 'AAAAAPAAJ%'
          AND All_Lists.al_absolute_path NOT LIKE 'AAAAAPAAC%'

Optimize SQL query with 2 selects


By : user2656661
Date : March 29 2020, 07:55 AM
like below fixes the issue I am trying to update a single campaign.id with minimum used_time (datetime) based on user.id but the following code need about 5 seconds to execute. Backlinks table contains 1 million rows. , You can try to UPDATE with JOIN by a subquery.
code :
UPDATE `backlinks` b
JOIN (
    SELECT c.id
    FROM campaigns c
    WHERE exists (
        SELECT 1 
        FROM campaigns cc
        WHERE c.user_id = cc.user_id
        GROUP BY cc.user_id
        HAVING min(cc.used_time) = c.used_time
    )
) t1 on b.`campaign_id` = t1.id
SET
    b.`crawler_id` = 'test', 
    b.`used_time`=NOW() 
WHERE 
    b.`googlebot_id` IS NULL 
AND 
    b.`used_time` IS NULL
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