Set operations with ORDER BY in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are set operations in SQL?

Set operations combine results from two or more SELECT queries into a single result. Common set operations include UNION, INTERSECT, and EXCEPT.

beginner

How does ORDER BY work with set operations?

ORDER BY sorts the final combined result of the set operation. It must be placed after all SELECT statements and set operators.

intermediate

Can you use ORDER BY inside each SELECT of a set operation?

No, ORDER BY inside individual SELECTs is ignored unless you use TOP or LIMIT. The final ORDER BY after the set operation controls sorting.

beginner

What happens if you use UNION without ORDER BY?

The combined result will have unique rows but the order is not guaranteed. To see sorted results, use ORDER BY after the UNION.

beginner

Write a simple SQL query using UNION and ORDER BY.

Example: SELECT name FROM students UNION SELECT name FROM teachers ORDER BY name ASC;

Where should ORDER BY be placed when using set operations like UNION?

A Between the SELECT statements

B After the last SELECT statement and set operation

C Before the first SELECT statement

D Inside each SELECT statement

ORDER BY must come after all SELECT statements and set operations to sort the final combined result.

What does UNION do in SQL?

A Combines results and removes duplicates

B Combines results and keeps duplicates

C Returns only common rows

D Returns rows from the first query only

UNION combines results from two queries and removes duplicate rows.

Can ORDER BY inside individual SELECT statements affect the final output order in a UNION?

A Yes, it controls the final order

B No, ORDER BY is ignored everywhere

C Yes, but only in some databases

D No, only the final ORDER BY after UNION affects order

ORDER BY inside individual SELECTs is ignored for final sorting; only the ORDER BY after the set operation matters.

Which set operation returns only rows common to both queries?

A INTERSECT

B UNION

C EXCEPT

D JOIN

INTERSECT returns only rows that appear in both queries.

What will happen if you omit ORDER BY after a UNION?

A Query will fail

B Result rows will be sorted by default

C Result rows will not be sorted

D Duplicates will appear

Without ORDER BY, the combined result has no guaranteed order.

Explain how to use ORDER BY with set operations like UNION in SQL.

Think about where the sorting happens after combining results.

Describe the difference between UNION and INTERSECT and how ORDER BY affects their results.

Focus on what rows each set operation returns and when sorting applies.