Quizzes – EduHub

Question 1

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

WHERE ORDER BY FILTER HAVING

Question 2

What is the purpose of the EXPLAIN statement in MySQL?

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

Question 3

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

FULL OUTER JOIN INNER JOIN LEFT JOIN RIGHT JOIN

Question 4

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

UNIQUE DISTINCT DIFFERENT EXCLUSIVE

Question 5

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

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

Question 6

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

SELECT, FROM, GROUP BY, WHERE, HAVING, ORDER BY SELECT, FROM, WHERE, HAVING, GROUP BY, ORDER BY FROM, SELECT, WHERE, GROUP BY, 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 Archive MyISAM InnoDB

Question 8

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

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

Question 9

What is the difference between CHAR and VARCHAR data types?

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

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

Question 11

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

Sum of all values in the table Total number of rows 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?

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

Question 13

What is the purpose of the ON DELETE CASCADE constraint?

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

Question 14

Which SQL statement is used to create a new database?

ADD DATABASE NEW DATABASE CREATE DATABASE MAKE DATABASE

Question 15

What does the IN operator do?

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

Question 16

Which clause is used to sort the result set?

ARRANGE BY GROUP BY SORT BY ORDER BY

Question 17

What is a subquery?

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

Question 18

Which of the following is true about indexes in MySQL?

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

Question 19

What is the result of SELECT NULL = NULL?

NULL Error TRUE FALSE

Question 20

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

CHANGE UPDATE MODIFY ALTER