Quiz for UNION vs UNION ALL

Q1: What is the difference between UNION and UNION ALL?

A. UNION includes duplicates B. UNION ALL sorts results C. UNION removes duplicates D. UNION ALL removes duplicates

Q2: What is the main difference between UNION and UNION ALL in SQL?

A. UNION removes duplicate records B. UNION ALL removes duplicates C. Both are identical D. UNION sorts results automatically

Q3: Which set operator is generally faster in execution?

A. UNION B. UNION ALL C. Both are equally fast D. None of the above

Q4: If you want to include duplicate rows in the result set, which operator should you use?

A. UNION B. MINUS C. INTERSECT D. UNION ALL

Q5: Which operator performs duplicate elimination automatically?

A. UNION B. UNION ALL C. JOIN D. EXCEPT

Q6: What is required for using UNION or UNION ALL between two SELECT statements?

A. Same number of columns and compatible data types B. Exact same column names C. Same table names D. Same WHERE clause

Q7: Which operator gives a larger result set if duplicates exist?

A. UNION B. INTERSECT C. UNION ALL D. MINUS

Q8: Can UNION and UNION ALL be used with different data types in corresponding columns?

A. Yes B. No C. Only UNION D. Only UNION ALL

Q9: Which operator will likely consume more memory when used on large datasets?

A. UNION B. UNION ALL C. MINUS D. JOIN

Q10: What happens if the column data types don’t match when using UNION?

A. An error is thrown B. Query executes but result is wrong C. Partial output is shown D. It removes unmatched columns

Q11: Which keyword is used to retain all duplicate records?

A. UNION DISTINCT B. UNION ALL C. UNION KEEP D. JOIN ALL

Q12: Which operator is suitable for merging results without checking for uniqueness?

A. UNION B. UNION ALL C. MERGE D. SELECT DISTINCT

Q13: Is column aliasing mandatory when using UNION or UNION ALL?

A. Yes B. No C. Only for UNION ALL D. Only for UNION

Q14: What is the order of precedence for set operators?

A. UNION > INTERSECT > MINUS B. INTERSECT > MINUS > UNION C. MINUS > UNION > INTERSECT D. All are equal

Q15: What clause can be used to sort the final output of a UNION query?

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

Q16: How do NULL values affect UNION and UNION ALL?

A. They are removed in UNION B. They are kept in UNION ALL C. They throw errors D. They are treated as empty strings

Q17: What happens if the SELECT statements in a UNION have different column counts?

A. UNION removes the extra columns B. SQL throws an error C. Only first SELECT is executed D. NULLs are padded

Q18: Which operator would you use to get a list of all employees and contractors, including duplicates?

A. UNION B. INTERSECT C. UNION ALL D. JOIN

Q19: Can you use ORDER BY in both SELECTs in a UNION?

A. Yes B. No C. Only in UNION ALL D. Only in UNION

Q20: What is true about UNION in terms of sorting?

A. Results are automatically sorted B. Sorting must be done using ORDER BY C. UNION does not allow sorting D. UNION ALL auto-sorts

Q21: To combine two SELECT queries and remove duplicates, use:

A. UNION ALL B. UNION C. JOIN D. GROUP BY