Quizzes – EduHub

Question 1

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

ORDER BY WHERE HAVING FILTER

Question 2

What is the purpose of the EXPLAIN statement in MySQL?

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

Question 3

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

RIGHT JOIN FULL OUTER JOIN INNER JOIN LEFT JOIN

Question 4

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

DIFFERENT DISTINCT EXCLUSIVE UNIQUE

Question 5

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

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

Question 6

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

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

Question 7

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

Memory InnoDB Archive MyISAM

Question 8

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

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

Question 9

What is the difference between CHAR and VARCHAR data types?

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

Question 10

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

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

Question 11

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

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

Question 12

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

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

Question 13

What is the purpose of the ON DELETE CASCADE constraint?

It prevents deletion of parent rows 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

Question 14

Which SQL statement is used to create a new database?

ADD DATABASE MAKE DATABASE CREATE DATABASE NEW DATABASE

Question 15

What does the IN operator do?

Checks if a value is NULL 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

Question 16

Which clause is used to sort the result set?

SORT BY ORDER BY ARRANGE BY GROUP BY

Question 17

What is a subquery?

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

Question 18

Which of the following is true about indexes in MySQL?

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

Question 19

What is the result of SELECT NULL = NULL?

FALSE NULL Error TRUE

Question 20

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

CHANGE MODIFY UPDATE ALTER