SQL UNION MCQ UNION and UNION ALL Practice Questions

Direction: Choose the correct option

What does UNION do?

A. Joins tables

B. Combines result sets, removes duplicates

C. Combines tables

D. Sorts results

Direction: Choose the correct option

SELECT city FROM customers UNION SELECT city FROM suppliers;

What will this return?

A. All cities with duplicates

B. Only supplier cities

C. Only customer cities

D. Unique cities from both

Direction: Choose the correct option

What's the difference between UNION and UNION ALL?

A. UNION ALL removes duplicates

B. Both same

C. UNION removes duplicates, UNION ALL keeps duplicates

D. UNION is faster

Direction: Choose the correct option

What rules must UNION queries follow?

A. Same number of columns, compatible data types

B. Same database

C. Any columns

D. Same table names

Direction: Choose the correct option

SELECT name, 'Customer' AS type FROM customers UNION SELECT name, 'Supplier' AS type FROM suppliers ORDER BY name;

Where is ORDER BY applied?

A. To each SELECT separately

B. To final combined result

C. Before UNION

D. Not allowed

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