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
4,475 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
1,070 reads
2016-11-15
1,325 reads
2016-05-31
1,604 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)
947 reads
2012-03-08
2,833 reads
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Question of the Day
The Disabled Index
I run this code on SQL Server 2022.
CREATE TABLE Drink
(
drinkid INT NOT NULL
CONSTRAINT DrinkPK PRIMARY KEY CLUSTERED,
drinkname VARCHAR(20),
rating NUMERIC(2, 1)
)
GO
INSERT INTO Drink
(
drinkid,
drinkname,
rating
)
VALUES
(1, 'Margarita', 4.5),
(2, 'Mojito', 4.3),
(3, 'Old Fashioned', 4.7),
(4, 'Martini', 4.4),
(5, 'Cosmopolitan', 4.2)
GO
ALTER INDEX drinkpk ON dbo.drink DISABLE
GO
SELECT * FROM dbo.Drink
GO
What is the result? See possible answers