Quiz for LEFT JOIN

Q1: What does LEFT JOIN return?

A. Only matching rows from both tables B. All rows from the right table C. All rows from the left table and matching from right D. Only non-matching rows

Q2: What does a LEFT JOIN return?

A. Only matching rows B. All rows from the right table C. All rows from the left table D. All rows from both tables

Q3: Which keyword is used to perform a LEFT JOIN in SQL?

A. LEFT OUTER JOIN B. INNER JOIN C. FULL JOIN D. CROSS JOIN

Q4: What is the result of LEFT JOIN if there is no match in the right table?

A. NULLs in right table columns B. Error C. Zero rows D. Duplicates in left table

Q5: Which of the following will return all records from Table A and matching ones from Table B?

A. SELECT * FROM A LEFT JOIN B B. SELECT * FROM A RIGHT JOIN B C. SELECT * FROM A INNER JOIN B D. SELECT * FROM A FULL JOIN B

Q6: What happens when LEFT JOIN is used and no matching row is found in the right table?

A. A default value is inserted B. Query fails C. NULL is returned D. Right table row is repeated

Q7: Which join type guarantees to include all rows from the left table?

A. INNER JOIN B. RIGHT JOIN C. LEFT JOIN D. CROSS JOIN

Q8: What does LEFT JOIN do when multiple matches are found in the right table?

A. Skips extra matches B. Returns only the first match C. Returns all matching rows D. Returns error

Q9: Which clause is necessary to define how the tables relate in a LEFT JOIN?

A. GROUP BY B. WHERE C. ON D. ORDER BY

Q10: If Table A has 5 rows and Table B has no matches, how many rows will a LEFT JOIN return?

A. 0 B. 5 C. 10 D. Depends on DB

Q11: Which SQL query is valid for LEFT JOIN?

A. SELECT * FROM A LEFT JOIN B ON A.id = B.a_id B. SELECT * FROM A LEFT JOIN B WHERE A.id = B.a_id C. SELECT * FROM A LEFT JOIN B A.id = B.a_id D. SELECT * FROM A JOIN B USING A.id

Q12: What does "LEFT OUTER JOIN" mean in SQL?

A. Return only common records B. Return unmatched right rows C. Same as LEFT JOIN D. Join without keys

Q13: What is the difference between LEFT JOIN and INNER JOIN?

A. LEFT JOIN excludes unmatched rows B. LEFT JOIN includes unmatched left rows C. INNER JOIN returns NULLs D. No difference

Q14: Can LEFT JOIN return more rows than the number of rows in the left table?

A. No B. Yes C. Only if keys are NULL D. Only on MySQL

Q15: How to filter only unmatched rows in LEFT JOIN?

A. Use GROUP BY clause B. Add WHERE right_table.column IS NULL C. Use FULL JOIN D. Add HAVING NULL condition

Q16: LEFT JOIN is used mostly to:

A. Fetch matching data only B. Fetch unmatched data from left table C. Ignore right table completely D. Avoid NULLs

Q17: What is a common use case of LEFT JOIN?

A. Combining two tables with same keys B. Fetching default values from the right table C. Showing records from one table even if there is no match D. Joining unrelated tables

Q18: LEFT JOIN is also known as:

A. Exclusive Join B. Optional Join C. Mandatory Join D. Duplicate Join

Q19: Which SQL clause should be used to filter rows after LEFT JOIN?

A. ON B. USING C. WHERE D. GROUP BY

Q20: Can LEFT JOIN be chained with other joins?

A. No B. Yes C. Only in MySQL D. Only in Oracle

Q21: Which is true about LEFT JOIN?

A. Requires primary key B. Returns only matched rows C. Can return unmatched rows from left table D. Always returns equal rows from both tables