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Very slow performance for inner join with restrictive where clause (very small subset of rows)

By : Stack Exchanger
Date : October 17 2020, 08:10 AM
it fixes the issue I had already rebuilt the index on t2 because it was fragmented. But I hadn't rebuilt the index on t1 or t_int since they looked fine.
to Mohammad Mohabbati's suggestion in the comments, I rebuilt them all and the query now runs in less than 1 second.
code :

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mysql slow performance on a small table with join query

By : user3618000
Date : March 29 2020, 07:55 AM
Hope this helps Try adding indexes on columns authors.last_name and authors.id.
But, are you sure your query is ok? shouldn't it look like :
code :
SELECT article.year, authors.last_name, count(DISTINCT article.id) as count FROM
article LEFT JOIN authors ON article.author_id = authors.id WHERE authors.last_name =
'bloggs' GROUP BY article.year

Simple Inner Join on 2 tables resulting in wrong estimated rows and slow performance

By : Dmitry Dubinsky
Date : March 29 2020, 07:55 AM
it should still fix some issue Non updated statistics might have something to do with it. Try running a exec sp_updatestats and see if the plan changes. Also make sure you have a maintenance job running on the SQL server that updates the statistics periodically.

Oracle sql how to join small number of rows with larger number of rows and not repeat small rows

By : misabiko
Date : March 29 2020, 07:55 AM
like below fixes the issue Row_number can be used to get sequence number an then case can be used to give empty name for person name for sequence >1
Also changed it to use explicit join
code :
   Select ( case when seq=1 then name else '' end ) as name,
   From (
      Select p.name,
         Row_number() over ( partition by p.person_id order by job_id desc) as seq
      from   people p
      Join jobs j
     On j.person_id = p.person_id) T

Left outer join and OR clause is slow. Is it possible to join after filtering?

By : F22 Raptor
Date : March 29 2020, 07:55 AM
will help you I have 2 tables like below. (1 million records in each table) When I join the two table and execute a query with OR clause, it is very slow. Is it possible that join the 2 tables ? , I would suggest union all:
code :
select *
from `tblA` a left outer join
     `tblB` b
      on a.name = b.name
where a.name = 'Alice'
union all 
select *
from `tblA` a inner join
     `tblB` b
      on a.name = b.name
where b.name = 'Alice' and a.name <> 'Alice'  -- got it in the first query;

How to speed up a slow multi-join query in a small Vertica database (~120K total rows, 10 minutes)

By : kamal
Date : March 29 2020, 07:55 AM
I wish this helpful for you First I see too many NO STATISTICS in your explain plan. That's a bad idea and you should fix it.
See the order of your tables in the join? A hash join was created and you're doing a full tbl scan on your biggest table. Fix this by doing hash join(small table join big table) and not (big table join small table).
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