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
4,324 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
1,064 reads
2016-11-15
1,314 reads
2016-05-31
1,595 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)
929 reads
2012-03-08
2,814 reads
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Which Result II
I have this code in SQL Server 2022:
CREATE SCHEMA etl;
GO
CREATE TABLE etl.product
(
ProductID INT,
ProductName VARCHAR(100)
);
GO
INSERT etl.product
VALUES
(2, 'Bee AI Wearable');
GO
CREATE TABLE dbo.product
(
ProductID INT,
ProductName VARCHAR(100)
);
GO
INSERT dbo.product
VALUES
(1, 'Spiral College-ruled Notebook');
GO
CREATE OR ALTER PROCEDURE etl.GettheProduct
AS
BEGIN
exec('SELECT ProductName FROM product;')
END;
GO
When I execute this code as a user whose default schema is dbo and has rights to the tables and proc, what is returned? See possible answers