SQL Learning Quizzes: Master Structured Query Language

Question 1

Which of the following is NOT a valid data type in SQL?

Accepted Answer

XML

Answer

INTEGER

Answer

VARCHAR(255)

Question 2

In SQL, which of the following is NOT a fundamental data type?

Accepted Answer

Array

Answer

Integer

Answer

Varchar

Answer

Boolean

Question 3

The primary purpose of the 'WHERE' clause in SQL is to:

Accepted Answer

Filter specific rows within a table

Answer

Establish a new table

Answer

Arrange rows in a table based on specific criteria

Answer

Remove rows from a table

Question 4

Which SQL function can provide the current date and time?

Accepted Answer

NOW()

Answer

DATE()

Answer

TIME()

Answer

DATETIME()

Question 5

What is the key distinction between a primary key and a foreign key in SQL?

Accepted Answer

A primary key uniquely identifies a row, while a foreign key references a primary key

Answer

A primary key ensures data integrity, while a foreign key establishes relationships between tables

Answer

A primary key must be unique, while a foreign key can contain null values

Answer

A primary key can be modified, but a foreign key cannot

Question 6

Which of the following SQL statements is syntactically correct for creating a table called 'Customers'?

Accepted Answer

CREATE TABLE Customers (ID INTEGER, Name VARCHAR(255), Email VARCHAR(255))

Answer

Customers TABLE CREATE (ID INTEGER, Name VARCHAR(255), Email VARCHAR(255))

Answer

CREATE Customers (ID INTEGER, Name VARCHAR(255), Email VARCHAR(255)) TABLE

Answer

TABLE Customers (ID INTEGER, Name VARCHAR(255), Email VARCHAR(255)) CREATE

Question 7

What is the primary benefit of using an index in SQL?

Accepted Answer

Enhanced query performance by minimizing data search time

Answer

Ensuring data integrity by preventing duplicate values

Answer

Establishing relationships between tables

Answer

Storing temporary data during query execution

Question 8

What result can be expected from the following SQL statement: SELECT COUNT(*) FROM Employees WHERE Salary > 50000

Accepted Answer

The count of employees with a salary exceeding $50,000

Answer

The average salary of employees

Answer

A list of employees earning more than $50,000

Answer

The maximum salary among all employees

Question 9

What is the purpose of a transaction in SQL?

Accepted Answer

Grouping a series of SQL statements into a single unit of work

Answer

Creating a database backup

Answer

Improving query performance by data caching

Answer

Preventing data loss in the event of system failure

Question 10

Which SQL function finds the largest value in a column?

Accepted Answer

MAX()

Answer

MIN()

Answer

AVG()

Question 11

In SQL, what is the primary function of the 'COMMIT' command?

Accepted Answer

Finalizes and saves all modifications made during the current transaction

Answer

Reverses all modifications made during the current transaction

Answer

Starts a new transaction

Answer

Temporarily stores a transaction for later execution

Question 12

To count the number of rows in an SQL table, which function should you use?

Accepted Answer

COUNT()

Answer

SUM()

Answer

AVG()

Question 13

In an SQL statement, which type of join is appropriate for combining two tables, 'Customers' and 'Orders', based on a common column, 'customer_id'?

Accepted Answer

INNER JOIN

Answer

LEFT JOIN

Answer

RIGHT JOIN

Answer

FULL OUTER JOIN

Question 14

Which of the following is the correct syntax to create a table named 'employees' with columns 'id' (int), 'name' (varchar(255)), and 'salary' (decimal(10,2))?

Accepted Answer

CREATE TABLE employees (id INT, name VARCHAR(255), salary DECIMAL(10,2))

Answer

CREATE TABLE employees (id VARCHAR(255), name INT, salary DECIMAL(10,2))

Answer

CREATE TABLE employees id INT, name VARCHAR(255), salary DECIMAL(10,2)

Answer

CREATE TABLE employees (id INT, name VARCHAR, salary DECIMAL)

Question 15

Which SQL command is used to add a new record to a table?

Accepted Answer

INSERT INTO

Answer

ADD

Answer

APPEND

Answer

CREATE

Question 16

Which technique is commonly used in SQL injection attacks?

Accepted Answer

Using single quotes to terminate a string and execute arbitrary SQL

Answer

Using special characters to escape string boundaries

Answer

Using parameterized queries

Answer

Using prepared statements

Question 17

Which SQL command grants specific permissions on a database object to a user?

Accepted Answer

GRANT

Answer

REVOKE

Answer

CREATE USER

Answer

ALTER USER

Question 18

Which SQL command would you use to select all rows from the 'Customers' table?

Accepted Answer

SELECT * FROM Customers

Answer

GET ALL FROM Customers

Answer

FETCH ALL FROM Customers

Answer

SHOW ALL FROM Customers

Question 19

What is the primary purpose of the WHERE clause in an SQL statement?

Accepted Answer

To filter rows based on a specific condition

Answer

To specify the columns to be retrieved

Answer

To group rows by a specified column

Answer

To sort the results in a specific order

Question 20

Which SQL data type should be used to store a numeric value that cannot have decimal places?

Accepted Answer

INT

Answer

FLOAT

Answer

VARCHAR

Answer

DATE

Question 21

What is the key difference between a primary key and a foreign key in an SQL table?

Accepted Answer

A primary key uniquely identifies a row within a table, while a foreign key references a primary key in another table

Answer

A foreign key uniquely identifies a row within a table, while a primary key references a foreign key in another table

Answer

Primary keys can contain duplicate values, while foreign keys cannot

Answer

Foreign keys can contain duplicate values, while primary keys cannot

Question 22

Which SQL function can be used to convert a text string to uppercase?

Accepted Answer

UPPER()

Answer

LOWER()

Answer

TRIM()

Answer

LEN()

Question 23

What is the primary purpose of using a JOIN operation in SQL?

Accepted Answer

To combine data from multiple tables based on a common field

Answer

To filter rows from a table based on a specific condition

Answer

To group rows from a table by a specified column

Answer

To sort the results of a query in a specific order

Question 24

Which SQL command would you use to create a new database named 'MyDatabase'?

Accepted Answer

CREATE DATABASE MyDatabase

Answer

MAKE DATABASE MyDatabase

Answer

NEW DATABASE MyDatabase

Answer

SET DATABASE MyDatabase

Question 25

What is the main advantage of creating an index in an SQL table?

Accepted Answer

To improve the speed of data retrieval by creating a searchable structure

Answer

To maintain data integrity by ensuring unique values

Answer

To store frequently used data in memory

Answer

To compress data to save storage space

Question 26

What is the primary distinction between an INSERT statement and an UPDATE statement in SQL?

Accepted Answer

INSERT adds new rows to a table, while UPDATE modifies existing rows

Answer

UPDATE adds new rows to a table, while INSERT modifies existing rows

Answer

INSERT modifies existing rows, while UPDATE adds new rows

Answer

Both INSERT and UPDATE add new rows to a table

Question 27

Which of the following is the primary purpose of the 'SELECT' statement in SQL?

Accepted Answer

To retrieve data from a table

Answer

To insert new records into a table

Answer

To update existing records in a table

Answer

To delete records from a table

Question 28

What is the key difference between a 'WHERE' clause and a 'HAVING' clause in SQL?

Accepted Answer

WHERE filters individual rows before grouping, while HAVING filters groups after grouping

Answer

HAVING filters rows before grouping, while WHERE filters groups after grouping

Answer

WHERE is used for filtering numeric values, while HAVING is used for filtering character values

Answer

They serve the same purpose and can be used interchangeably

Question 29

What is the main purpose of using an 'INNER JOIN' in SQL?

Accepted Answer

To combine rows from multiple tables based on a common column

Answer

To exclude rows from a table based on a condition

Answer

To create a new table by combining data from multiple tables

Answer

To update rows in a table based on a condition

Question 30

What is the purpose of using a 'PRIMARY KEY' constraint in a SQL table?

Accepted Answer

To ensure that each row in the table has a unique value for the specified column(s)

Answer

To prevent null values from being inserted into the specified column(s)

Answer

To create an index on the specified column(s)

Answer

To enforce a foreign key relationship with another table

Question 31

Which SQL statement is used to modify the structure of an existing table?

Accepted Answer

ALTER TABLE

Answer

MODIFY TABLE

Answer

UPDATE TABLE

Answer

CHANGE TABLE

Question 32

What is the primary purpose of using an 'INDEX' in SQL?

Accepted Answer

To improve query performance by quickly locating rows based on specified column(s)

Answer

To ensure that data in the table is stored in a specific order

Answer

To prevent duplicate values from being inserted into the table

Answer

To create a relationship between two tables

Question 33

Which of the following SQL commands is used to create a new database named 'my_database'?

Accepted Answer

CREATE DATABASE my_database

Answer

CREATE TABLE my_database

Answer

NEW DATABASE my_database

Answer

MAKE DATABASE my_database

Question 34

What is the primary purpose of the 'SELECT' statement in SQL?

Accepted Answer

To retrieve data from a table

Answer

To create a new table

Answer

To update data in a table

Answer

To delete data from a table

Question 35

Which SQL data type is used to store whole numbers?

Accepted Answer

INTEGER

Answer

FLOAT

Answer

DECIMAL

Answer

VARCHAR

Question 36

What is the difference between a 'PRIMARY KEY' and a 'FOREIGN KEY' in SQL?

Accepted Answer

A primary key identifies a unique row, while a foreign key references a primary key in another table

Answer

A foreign key identifies a unique row, while a primary key references a foreign key in another table

Answer

Both primary keys and foreign keys can be used to create relationships between tables

Answer

Primary keys and foreign keys are interchangeable terms

Question 37

What is the purpose of a 'JOIN' operation in SQL?

Accepted Answer

To combine rows from multiple tables based on a common column value

Answer

To create a new table from existing tables

Answer

To update data in multiple tables

Answer

To delete data from multiple tables

Question 38

In SQL database security, which statement accurately describes the difference between authentication and authorization?

Accepted Answer

Authentication verifies the user's identity, while authorization determines their access to specific database resources.

Answer

Authorization verifies the user's identity, while authentication determines their access to specific database resources.

Answer

Both authentication and authorization verify the user's identity.

Answer

Both authentication and authorization determine the user's access to specific database resources.

Question 39

How does indexing speed up SQL queries?

Accepted Answer

Indexing creates a structured way to organize data, allowing for faster retrieval.

Answer

Indexing is most helpful for databases with a large amount of data.

Answer

Creating indexes on every column isn't always necessary for optimal performance.

Question 40

What is the main function of the 'GROUP BY' clause in SQL?

Accepted Answer

Grouping rows with matching values

Answer

Sorting the results in a specific order

Answer

Filtering the results based on criteria

Question 41

Which SQL command is used to create a new table?

Accepted Answer

CREATE TABLE

Answer

ADD TABLE

Answer

ALTER TABLE

Answer

CREATE COLUMN

Question 42

What is the purpose of the 'WHERE' clause in an SQL statement?

Accepted Answer

To filter rows based on a specified condition

Answer

To update the data in the table

Answer

To sort the results in ascending order

Answer

To group the results by a specific column

Question 43

Which data type is used to store dates and times in SQL?

Accepted Answer

DATETIME

Answer

INTEGER

Answer

FLOAT

Answer

VARCHAR

Question 44

What is the difference between an inner join and an outer join?

Accepted Answer

An inner join returns only matching rows, while an outer join returns all rows from one table and any matching rows from the other table.

Answer

An inner join returns all rows from both tables, while an outer join returns only matching rows.

Question 45

Which SQL function is used to calculate the average of a set of values?

Accepted Answer

AVG

Answer

COUNT

Answer

SUM

Question 46

What is the purpose of using indexes in SQL?

Accepted Answer

To improve query performance by quickly locating data

Answer

To enforce data integrity

Answer

To store duplicate data

Question 47

Which SQL statement is used to update data in a table?

Accepted Answer

UPDATE

Answer

DELETE

Answer

INSERT

Answer

SELECT

Question 48

What is the output of the following SQL query: SELECT * FROM table_name WHERE column_name LIKE '%search term%';

Accepted Answer

Rows where the value in the specified column contains the search term

Answer

Rows where the value in the specified column is equal to the search term

Answer

Rows where the value in the specified column starts with the search term

Question 49

Which SQL command is used to delete records from a table?

Accepted Answer

DELETE

Answer

SELECT

Answer

INSERT

Answer

UPDATE

Question 50

Which data constraint is used to ensure that a column contains unique values?

Accepted Answer

UNIQUE

Answer

NOT NULL

Answer

DEFAULT