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 explain the syntax of a query To display the execution plan 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?

FULL OUTER JOIN INNER JOIN RIGHT JOIN LEFT JOIN

Question 4

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

EXCLUSIVE DIFFERENT UNIQUE DISTINCT

Question 5

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

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

Question 6

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

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

Question 7

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

MyISAM Memory Archive InnoDB

Question 8

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

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

Question 9

What is the difference between CHAR and VARCHAR data types?

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

Question 10

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

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

Question 11

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

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

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

CREATE DATABASE NEW DATABASE MAKE DATABASE ADD DATABASE

Question 15

What does the IN operator do?

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

Question 16

Which clause is used to sort the result set?

ORDER BY ARRANGE BY SORT BY GROUP BY

Question 17

What is a subquery?

A query that is executed before the main query A query that returns multiple rows 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 speed up INSERT operations They slow down SELECT queries They are automatically created on all columns They can speed up search queries but slow down writes

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?

MODIFY UPDATE CHANGE ALTER