UNION

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UNION vs. UNION ALL in SQL Server

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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

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Question of the Day

Adding new column with DEFAULT

Which number will the COUNT() return after executing the following statements: 

DROP TABLE IF EXISTS #test;
CREATE TABLE #test (id INT)
INSERT INTO #test (id)
SELECT *
  FROM GENERATE_SERIES(1, 3) AS gs
;

ALTER TABLE #test ADD flag BIT CONSTRAINT DF_#test_flag DEFAULT 0;
go
UPDATE #test SET flag = 0 WHERE id = 1
UPDATE #test SET flag = 1 WHERE id = 2

INSERT INTO #test (id) VALUES (4)

SELECT COUNT(*)
  FROM #test AS t
 WHERE flag = 0
 

See possible answers