How to Order Results from Multiple SELECT Statements Combined with UNION?

Sorting Combined SELECT Statement Results using UNION

The UNION operator combines results from multiple SELECT statements. While you might expect to order the final result set with a single ORDER BY clause, this isn't directly supported. The ORDER BY clause must be applied to the entire combined result set.

Here's the correct approach:

<code class="language-sql">SELECT id, name, age
FROM Student
WHERE age < 20
UNION
SELECT id, name, age
FROM Student
WHERE age >= 20
ORDER BY age;</code>

By placing ORDER BY age after the final SELECT statement, the sorting is applied to the unified output, correctly ordering all rows by the age column. This ensures proper ordering after the data from both queries has been merged.

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