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AI-assisted, automatically checked• Updated August 2026

SQL Joins MCQs

Test your understanding of INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN, and CROSS JOIN.

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Deep-dive into Joins principles within SQL. These targeted questions evaluate edge-cases, common pitfalls, and interview problem patterns.

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Joins MCQ Questions

Page 1 of 1 (5 total)
Q1

What is the difference between a full outer join and an inner join?

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View Answer & Explanation
Correct Answer: A full outer join returns all rows from both tables, filling in NULLs where there is no match, while an inner join returns only rows with matches in both tables
Explanation:
Because a full outer join keeps unmatched rows from both sides, it is useful when you want to see everything, including records that have no corresponding match in the other table.
Q2

What is the purpose of using aliases with the SQL 'AS' keyword in a JOIN query?

easy
View Answer & Explanation
Correct Answer: It gives shorter or more readable names to tables or columns, making complex joins easier to write and read
Explanation:
Aliases are especially useful when a query joins the same table to itself, since each reference to the table needs its own distinct name to avoid ambiguity.
Q3

Which JOIN returns all rows from the left table and matching rows from the right table, filling with NULL where there is no match?

easy
View Answer & Explanation
Correct Answer: LEFT JOIN
Explanation:
LEFT OUTER JOIN (or LEFT JOIN) returns all records from the left table and matched records from the right table. If no match exists, NULL is returned for right table columns.
Q4

Which join returns all rows from the left table, and matching rows from the right table, filling nulls if no match exists?

easy
View Answer & Explanation
Correct Answer: LEFT JOIN
Explanation:
A LEFT (OUTER) JOIN returns all rows from the left table regardless of whether there is a corresponding match in the right table.
Q5

What is the Cartesian product join of two tables with M and N rows respectively?

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View Answer & Explanation
Correct Answer: M * N rows via CROSS JOIN
Explanation:
A CROSS JOIN produces the Cartesian product of two tables, resulting in M * N rows.