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
4,353 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
1,315 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
2,816 reads
Blogs
AI: Blog a Day – Day 4: Transformers – Encoder, Decoder, and Attention
By Vinay Thakur
Continuing from Day 3 where we covered LLM models open/closed and their parameters, Today...
Flyway Tips: Multiple Projects
By Steve Jones
One of the nice things about Flyway Desktop is that it helps you manage...
What DevOps Look Like in Microsoft Fabric
By HeyMo0sh
Microsoft Fabric (not to be confused with the more general term “fabric” in DevOps)...
Forums
Can an Azure App Service Managed Identity be used for SQL Login?
I'm fairly certain I know the answer to this from digging into it yesterday,...
Azure Synapse database refresh
Hi Team, I am trying to refresh the Azure Synapse Dedicated pool from production...
how to write this query?
hi everyone I am not sure how to write the query that will produce...
Question of the Day
Fun with JSON I
I have some data in a table:
CREATE TABLE #test_data
(
id INT PRIMARY KEY,
name VARCHAR(100),
birth_date DATE
);
-- Step 2: Insert rows
INSERT INTO #test_data
VALUES
(1, 'Olivia', '2025-01-05'),
(2, 'Emma', '2025-03-02'),
(3, 'Liam', '2025-11-15'),
(4, 'Noah', '2025-12-22');
If I run this query, how many rows are returned?
SELECT *
FROM OPENJSON(
(
SELECT t.* FROM #test_data AS t FOR JSON PATH
)
) t; See possible answers