Understanding UNION and UNION ALL in SQL Server
A short look at the differences in UNION and UNION ALL in a SELECT query.
2025-04-07
4,362 reads
UNION
UNION vs. UNION ALL in SQL Server
Sometimes there is a need to combine data from multiple tables or views into one comprehensive dataset. This may be for like tables within the same database or maybe there is a need to combine like data across databases or even across servers. I have read about the UNION and UNION ALL commands, but how do these work and how do they differ?
2019-12-05
2018-06-12
1,065 reads
2016-11-15
1,317 reads
2016-05-31
1,596 reads
Union Forcing Distinct
The use of union would seem to force a distinct in each of the select statements being unioned. The use multiple unions, with mixed union and union all clauses, seems to cause haphazard results.
2013-05-14 (first published: 2013-04-30)
932 reads
2012-03-08
2,817 reads
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Question of the Day
Identity Defaults
What happens when I run this code?
CREATE TABLE dbo.IdentityTest
(
id int IDENTITY(10) PRIMARY KEY,
somevalue VARCHAR(20)
)
GO
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