Sep 8, 2008 · UNION removes duplicate rows (where all columns in the results are the same), UNION ALL does not.. There is a performance hit when using UNION instead of UNION ALL, since the database server must do additional work to remove the duplicate rows, but usually you do not want the duplicates (especially when developing reports).

Mar 25, 2011 · or using CTE (SQL Server 2005+);with One as ( select top 2 t1.ID, t1.ReceivedDate from Table t1 where t1.Type = 'TYPE_1' order by t1.ReceivedDate de ) ,Two as ( select top 2 t2.ID from Table t2 where t2.Type = 'TYPE_2' order by t2.ReceivedDate desc ) select * from One union select * from Two

Jan 17, 2014 · UNION will always eliminate rows that are duplicated between queries. In order to do this efficiently, the server must sort the rows first. UNION ALL allows duplicates, and so no inter-query sorting is required. The server improves performance by not doing the unnecessary sorting, unless you specify an ORDER BY clause. –

Nov 1, 2012 · DECLARE @tmpValue SET @tmpValue = 0 -- it will be change SELECT * FROM Animal WHERE AniActive = 1 UNION SELECT * FROM Animal WHERE 1 = CASE WHEN @tmpValue = 0 THEN 0 ELSE Active = 1 END your situation is not to complex but for more complex condition you can use nested CASE statement in Query .

You do not need a UNION for that - replacing an inner join with a pair of outer ones should do it:. UPDATE c SET c.order_status = 1 FROM Customer AS c LEFT OUTER JOIN Order_Web As ow ON c.id = ow.customer_id LEFT OUTER JOIN Order As o ON c.id = o.customer_id WHERE ow.order_filled = 1 OR o.order_filled = 1

Mar 21, 2023 · SELECT A FROM ( SELECT A, B FROM TableA UNION SELECT A, B FROM TableB ) WHERE B > 'some value' Am I missing anything or making an assumption about how this works? I'm using MSSQL 2005 so any solution will need to conform to what I can do there.

Apr 10, 2016 · If you are trying to union multiple CTEs, then you need to declare the CTEs first and then use them: With Clients As ( Select Client_No From dbo.Decision_Data Group By Client_No Having Count(*) = 1 ) , CTE2 As ( Select Client_No From dbo.Decision_Data Group By Client_No Having Count(*) = 2 ) Select Count(*) From Decision_Data Union Select Count(Distinct Client_No) From dbo.Decision_Data Union ...

Feb 25, 2016 · What happens is, The query with Union All and Distinct will take CPU cost more than Query with Union. Performance on Time: UNION ALL: (1172 row(s) affected) SQL Server Execution Times: CPU time = 0 ms, elapsed time = 39 ms. UNION: (1172 row(s) affected) SQL Server Execution Times: CPU time = 10 ms, elapsed time = 25 ms.

Mar 20, 2017 · I'm doing a UNION of two queries on an Oracle database. Both of them have a WHERE clause. Is there a difference in the performance if I do the WHERE after UNIONing the queries compared to performing the UNION after WHERE clause? For example: SELECT colA, colB FROM tableA WHERE colA > 1 UNION SELECT colA, …

Per the SQL Standard, the order of results is undefined barring an explicit order by clause. That first select in your example probably returns its results in the order returned by the subselect, but it is not guaranteed. Further, that does *not* guarantee the ordering of the result set of the entire union (same rule in the Standard). If you ...