Quiz for Rules & Requirements

Q1: What is required for using SQL set operators like UNION and INTERSECT?

A. Only numeric data types B. Both queries must have the same number of columns and data types C. Same primary key D. Same WHERE clause

Q2: Which requirement must be met when using UNION in SQL?

A. The SELECT statements must have the same number of columns. B. The column names must be identical. C. Only one SELECT statement can be used. D. The result set must be sorted.

Q3: What is a key rule when combining queries using INTERSECT?

A. Queries must select from the same table. B. The data types of columns must match. C. Each query must have a WHERE clause. D. INTERSECT requires ORDER BY in all queries.

Q4: What happens if the number of columns doesn’t match in a UNION?

A. The result is automatically adjusted. B. Extra columns are ignored. C. An error is thrown. D. The UNION becomes a JOIN.

Q5: Which SQL set operator does not eliminate duplicate rows by default?

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

Q6: What must be true about the data types of columns in a set operator?

A. They must be identical in name. B. They must have the same data type or be compatible. C. They can be in any order. D. Only one column is required to match.

Q7: Can you use ORDER BY in individual queries in a UNION operation?

A. Yes, it is required. B. Yes, in each subquery. C. No, ORDER BY must be in the final query only. D. No, ORDER BY is not allowed at all.

Q8: What is returned by INTERSECT in SQL?

A. All unique rows from both queries. B. Only duplicate rows across both queries. C. All rows from the first query. D. All rows from the second query.

Q9: Which of the following operators automatically removes duplicates?

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

Q10: What does the MINUS operator return?

A. Common records from two queries. B. Only unique records from both queries. C. Records present in the first query but not in the second. D. All records from both queries.

Q11: Which set operator preserves duplicates?

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

Q12: Why must the column count match in set operations?

A. To maintain table normalization. B. To avoid join errors. C. Set operators compare row by row by position. D. To simplify query parsing.

Q13: What happens if the data types do not match in a UNION?

A. The query returns no rows. B. It automatically converts types. C. It throws an error. D. It performs a cartesian product.

Q14: Which clause is only allowed once in a set operation query?

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

Q15: Can you use JOINs within a set operation query?

A. Yes, in each SELECT statement. B. No, joins are not allowed. C. Only in UNION ALL. D. Only for MINUS.

Q16: Which set operator is not supported in some databases like MySQL?

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

Q17: Why might you prefer UNION ALL over UNION?

A. It is faster since it skips duplicate elimination. B. It enforces schema rules. C. It prevents SQL injection. D. It sorts the data automatically.

Q18: Which of the following is NOT a valid SQL set operator?

A. UNION B. INTERSECT C. EXCEPT D. MERGE

Q19: What does EXCEPT do in PostgreSQL?

A. Returns all rows from both queries. B. Returns common rows. C. Returns rows in the first query but not in the second. D. Returns rows from the second query.

Q20: Are column names required to match in set operators?

A. Yes, always. B. No, but the number and types must match. C. Only for INTERSECT. D. Only if ORDER BY is used.

Q21: How is column alignment determined in UNION?

A. By name. B. By position. C. By alias. D. By data type only.