MySQL - Subqueries MCQ

MySQL – Subqueries MCQ

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1. What is a subquery in MySQL?

An independent query within another query

A primary key column

A nested table

A foreign key constraint

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2. What is the primary purpose of using subqueries in SQL?

To perform complex operations

To retrieve data from a single table

To sort data

To filter data

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3. What are the two primary types of subqueries in MySQL?

INNER and OUTER

Nested and Independent

Correlated and Non-Correlated

Primary and Secondary

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4. In a correlated subquery, what does the inner query reference?

Columns from other tables

Columns from the outer query

Constants

Row numbers

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5. How many times does a correlated subquery execute in MySQL?

Once for the entire query

Once for each row in the outer query

Twice for each row in the outer query

It depends on the number of tables involved

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6. When might you use a correlated subquery in SQL?

To aggregate data

To perform row-level comparisons

To retrieve rows based on a specific condition

To calculate the maximum value

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7. In a non-correlated subquery, how many times does the inner query execute?

It depends on the number of tables involved

Twice for each row in the outer query

Once for each row in the outer query

Once for the entire query

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8. What is the primary use of a non-correlated subquery?

To reference columns from the outer query

To retrieve data from multiple tables

To perform row-level comparisons

To calculate an average value

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9. Which part of a SQL statement can contain a subquery?

SELECT clause

FROM clause

WHERE clause

ORDER BY clause

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10. What does a correlated subquery in the WHERE clause allow you to do?

Filter rows based on a specific condition

Calculate averages

Sort rows

Retrieve data from multiple tables

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11. In a subquery within the SELECT clause, what does the result of the subquery represent?

A value for each row in the main query

A single row from a table

A constant value

The result of an aggregation

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12. How can you improve the performance of correlated subqueries in MySQL?

Use them in the SELECT clause

Avoid using subqueries altogether

Use them for simple operations

Ensure proper indexing

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13. What is the primary purpose of using aliases in subqueries?

To create new tables

To filter data

To sort data

To simplify queries

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14. When using subqueries, what is an alias?

A secondary table

A temporary table

A database schema

A shorthand name for a column

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15. Which type of subquery is more efficient in terms of execution?

Non-correlated subqueries

It depends on the specific use case

Both types are equally efficient

Correlated subqueries

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16. What is the primary advantage of using subqueries in SQL?

Creating new tables

Sorting data

Reducing the number of tables

Simplifying complex operations

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17. In a subquery within the FROM clause, what does the subquery provide?

A single value

An independent dataset

Constants

A temporary table

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18. What is the primary purpose of subqueries in the SELECT clause?

To perform calculations on columns

To sort data

To create new tables

To filter rows based on conditions

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19. When using subqueries in SQL, what should you consider to maintain code readability?

Using subqueries only in the FROM clause

Using subqueries for all operations

Providing meaningful aliases

Avoiding subqueries altogether

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20. What type of subquery is used when the inner query is independent of the outer query?

Aggregate subquery

Non-correlated subquery

Nested subquery

Correlated subquery

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21. How can you use subqueries in the SELECT clause to retrieve a specific piece of data?

By retrieving a single value from the inner query

By using an alias

By joining multiple tables

By using the HAVING clause

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22. What is the primary purpose of non-correlated subqueries in SQL?

To perform row-level comparisons

To reference columns from the outer query

To calculate averages

To aggregate data

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23. What does the result of a subquery within the WHERE clause affect?

The filtering of rows based on conditions

The number of rows returned in the result set

The order of columns in the result set

The grouping of rows

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24. Which SQL clause allows you to specify conditions for filtering rows in subqueries?

HAVING clause

GROUP BY clause

WHERE clause

SELECT clause

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25. In a subquery within the SELECT clause, what does the result of the subquery often represent?

A constant value

A single row from a table

A value for each row in the main query

The maximum value

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