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How to use Union and Group By in MS SQL?


I found some problem using Union and Group By clause together, and I later realized that my technique of using these words together is not proper.
Most of the users are making the same mistakes when they deal with Union and Group By clause.
You can use like below:
SELECT x FROM (
SELECT x FROM table_A
UNION
SELECT x FROM table_B
)
GROUP BY x;

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