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Two queries with same tables and join logic but different results


By : Kerm Steffenhagen
Date : October 16 2020, 08:10 PM
I hope this helps . I am trying to get records only in 1 table i.e in A but not in B case1: , If using NOT IN you must not allow NULL as a value of the "in list"
code :
SELECT count(DISTINCT t.col1)
FROM `table2_ * ` AS t
WHERE t._table_suffix BETWEEN '20180101' AND '20181231'
 AND col1 NOT IN (
  SELECT DISTINCT e.col1
  FROM `table1` AS e
  WHERE DATE (timestamp_seconds(e.ts)) >= '2018-01-01'
   AND e.col1 IS NOT NULL
  );
SELECT count(DISTINCT t.col1)
FROM `table2_ * ` AS t
WHERE t._table_suffix BETWEEN '20180101' AND '20181231'
 AND NOT EXISTS (
  SELECT NULL
  FROM `table1` AS e
  WHERE DATE (timestamp_seconds(e.ts)) >= '2018-01-01'
   AND e.col1 = t.col1
  );


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Which of the following SQL queries would be faster? A join on two tables or successive queries?


By : Harvi
Date : March 29 2020, 07:55 AM
Hope that helps Every query has overhead. If you can do something with one query, it's (almost) always better to do it with one query. And most database engines are smarter than you. Even if it's better to split a query in some way, the database will find out himself.
An example of overhead: if you perform 100 queries, there will be a lot more traffic between your application and your webserver.

Join two queries into one in order to join the results


By : guyk
Date : March 29 2020, 07:55 AM
will be helpful for those in need I have a small sql question for you. , try the following inner join:
code :
SELECT tbl_CostPrevisions.Month, SUM(tbl_CostPrevisions.Value) AS 'COST' , SUM(tbl_IncomePrevisions.Value) AS 'INCOME'
FROM tbl_CostPrevisions
INNER JOIN tbl_IncomePrevisions on tbl_CostPrevisions.Month = tbl_IncomePrevisions.Month
WHERE tbl_CostPrevisions.Year = @YEAR AND tbl_IncomePrevisions.Year = @YEAR
GROUP BY tbl_CostPrevisions.Month

sqlite / websql: separate queries produce different results than join queries


By : ak3n
Date : March 29 2020, 07:55 AM
I wish this help you When you list two tables A and B in the FROM clause, you get a cross join, which returns A×B records. So if one table is empty, the result will be empty, too.
To ensure that you have a record even for an empty table, add another record with UNION ALL, then use LIMIT 1 return the first record. For example,
code :
SELECT Name, PW FROM UserData
UNION ALL
SELECT NULL, NULL
LIMIT 1
SELECT *
FROM (SELECT Name, PW FROM UserData
      UNION ALL
      SELECT NULL, NULL
      LIMIT 1),
     Prefs

Using binary logic in PostgreSQL JOIN queries


By : aerosmile
Date : March 29 2020, 07:55 AM
I wish this helpful for you I've got 3 tables that look vaguely like this: , You could use a UNION in this case
code :
SELECT users.NAME
    ,users.phone
    ,user_groups.activity
FROM users
INNER JOIN group_membership ON group_membership.userID = users.userID
INNER JOIN user_groups ON user_groups.groupID = group_membership.groupID
WHERE user_groups.activity = 'Knitting'

UNION

SELECT users.NAME
    ,users.phone
    ,independent_activity.activity
FROM users
INNER JOIN independent_activity ON independent_activity.userID = users.userID
WHERE independent_activity.activity = 'Knitting';

Join two queries that are grouped by same column from same tables but different parameters to join


By : C. Van de Poel
Date : March 29 2020, 07:55 AM
it should still fix some issue I have 3 tables with items, owners and statuses and I need to show the count of items that were sold/discarded grouped by every owner for the year passed as parameter. , Move your status filter to case statements in your select clause.
code :
select      o.pk_owner_id,
            SaleCount = count(case when i.fkl_status_ID = 1 then 1 end),
            DiscardCount = count(case when i.fkl_item_status_ID = 2 then 1 end)
from        Status s 
join        Item i on s.fkl_item_ID = i.pk_item_ID
join        Owner o on s.fkl_owner_ID = o.pk_owner_ID                   
where       o.isactive = 1 
and         year(i.dtList_Date) = @QueryYear 
group by    o.pk_owner_id
and i.fkl_status_ID in (1,2)
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