Quizzes – EduHub

Question 1

Which SQL clause is used to filter rows after aggregation in a GROUP BY query?

FILTER HAVING ORDER BY WHERE

Question 2

What is the purpose of the EXPLAIN statement in MySQL?

To display the execution plan of a query To explain the syntax of a query To create an index To execute a query and show results

Question 3

Which join returns all rows when there is a match in one of the tables?

INNER JOIN RIGHT JOIN FULL OUTER JOIN LEFT JOIN

Question 4

Which of the following is used to avoid duplicate rows in a SELECT result?

UNIQUE EXCLUSIVE DISTINCT DIFFERENT

Question 5

What does the following SQL do? CREATE INDEX idx_name ON table (column);

Creates a primary key Creates a unique constraint Creates a foreign key Creates an index for faster searches

Question 6

Which of the following is the correct order of clauses in a SELECT statement?

SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY SELECT, FROM, WHERE, HAVING, GROUP BY, ORDER BY FROM, SELECT, WHERE, GROUP BY, HAVING, ORDER BY SELECT, FROM, GROUP BY, WHERE, HAVING, ORDER BY

Question 7

What is the default storage engine in MySQL (as of version 8.0)?

Archive InnoDB Memory MyISAM

Question 8

Which SQL function returns the number of characters in a string?

CHAR_LENGTH() COUNT() SIZE() LENGTH()

Question 9

What is the difference between CHAR and VARCHAR data types?

Both are variable-length Both are fixed-length CHAR is variable-length, VARCHAR is fixed-length CHAR is fixed-length, VARCHAR is variable-length

Question 10

Which of the following is used to add a new column to an existing table?

ALTER TABLE ... ADD COLUMN INSERT TABLE ... ADD COLUMN UPDATE TABLE ... ADD COLUMN MODIFY TABLE ... ADD COLUMN

Question 11

What does the following query return? SELECT COUNT(*) FROM table;

Sum of all values in the table Number of non-null values in all columns Average of all values Total number of rows in the table

Question 12

Which of the following is a valid way to delete all rows from a table without removing the table structure?

DELETE FROM table; DROP TABLE table; Both A and B are correct TRUNCATE TABLE table;

Question 13

What is the purpose of the ON DELETE CASCADE constraint?

It updates child rows when parent is deleted It deletes the parent row when a child row is deleted It deletes child rows when the parent row is deleted It prevents deletion of parent rows

Question 14

Which SQL statement is used to create a new database?

MAKE DATABASE CREATE DATABASE ADD DATABASE NEW DATABASE

Question 15

What does the IN operator do?

Checks if a value matches any value in a list Checks if a value is within a range Checks if a value exists in a subquery Checks if a value is NULL

Question 16

Which clause is used to sort the result set?

GROUP BY SORT BY ORDER BY ARRANGE BY

Question 17

What is a subquery?

A query nested inside another query A query that returns multiple rows A query that uses the UNION operator A query that is executed before the main query

Question 18

Which of the following is true about indexes in MySQL?

They speed up INSERT operations They are automatically created on all columns They can speed up search queries but slow down writes They slow down SELECT queries

Question 19

What is the result of SELECT NULL = NULL?

NULL FALSE Error TRUE

Question 20

Which of the following SQL commands is used to change data in an existing row?

UPDATE ALTER CHANGE MODIFY