SQL Basics: Master the Fundamentals of SQL Programming

Question 1

Which SQL command is primarily used to retrieve data from a table?

Accepted Answer

SELECT

Answer

INSERT

Answer

UPDATE

Answer

DELETE

Question 2

Consider the following table creation syntax: 'CREATE TABLE Customers (ID int, Name varchar(255), Address varchar(255));'. Which option represents the correct syntax?

Accepted Answer

CREATE TABLE Customers (ID int, Name varchar(255), Address varchar(255));

Answer

CREATE TABLE 'Customers' (ID int, Name varchar(255), Address varchar(255));

Answer

CREATE TABLE Customers {ID int, Name varchar(255), Address varchar(255);}

Answer

CREATE 'Customers' TABLE (ID int, Name varchar(255), Address varchar(255));

Question 3

Which data type is most suitable for storing a customer's name?

Accepted Answer

varchar(255)

Answer

int

Answer

datetime

Answer

boolean

Question 4

In an SQL statement, what is the primary purpose of the WHERE clause?

Accepted Answer

To specify conditions for row selection

Answer

To determine the order in which rows are displayed

Answer

To group rows based on a specific column

Answer

To modify data within a table

Question 5

Which operator is used in SQL to compare two values?

Accepted Answer

=

Answer

+

Answer

>

Answer

%

Question 6

Consider the following SQL statement: 'UPDATE Customers SET Name = 'John' WHERE ID = 1'. What is the intended outcome?

Accepted Answer

Updates the name of the customer with ID 1 to 'John'

Answer

Creates a new customer named 'John'

Answer

Deletes the customer with ID 1

Answer

Displays the updated customer information

Question 7

Which SQL command is employed to permanently remove a table from a database?

Accepted Answer

DROP

Answer

DELETE

Answer

TRUNCATE

Answer

ALTER

Question 8

Can you differentiate between a primary key and a foreign key?

Accepted Answer

A primary key uniquely identifies each row, while a foreign key establishes a connection to another table.

Answer

A foreign key uniquely identifies each row, while a primary key establishes a connection to another table.

Answer

Both primary and foreign keys serve the same purpose of row identification.

Answer

Both primary and foreign keys are used for data integrity but in different ways.

Question 9

Within the context of SQL, which of the following is NOT a valid data type?

Accepted Answer

array

Answer

int

Answer

varchar

Answer

datetime

Question 10

What is the main purpose of an ORDER BY clause in SQL?

Accepted Answer

Arranging the result set in ascending or descending order

Answer

Grouping the result set based on a particular column

Answer

Filtering the result set based on specified criteria

Answer

Limiting the number of rows returned

Question 11

In SQL, which command is used to create a new table?

Accepted Answer

CREATE

Answer

SELECT

Answer

INSERT

Answer

UPDATE

Question 12

Which of the following is **not** a data manipulation command in SQL?

Accepted Answer

CREATE

Answer

SELECT

Answer

UPDATE

Answer

DELETE

Question 13

What is the purpose of the 'ALTER' command in SQL?

Accepted Answer

Adds or modifies columns in a table

Answer

Creates a new database

Answer

Updates data in a table

Answer

Deletes a table

Question 14

Which of the following is the correct syntax to create a new table named 'employees' with three columns ('id', 'name', 'salary') using the correct data types?

Accepted Answer

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

Answer

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

Answer

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

Answer

CREATE TABLE employees (id, name, salary)

Question 15

What is the result of the following SQL query: 'SELECT * FROM employees WHERE salary > 50000'?

Accepted Answer

Retrieves all employees with a salary greater than $50,000

Answer

Updates all employees with a salary greater than $50,000

Answer

Creates a new table with employees earning more than $50,000

Answer

Deletes all employees with a salary greater than $50,000

Question 16

Which of the following data types is used to store numeric values with decimal precision?

Accepted Answer

DECIMAL

Answer

INTEGER

Answer

FLOAT

Answer

VARCHAR

Question 17

What is the primary purpose of a foreign key constraint?

Accepted Answer

To ensure data integrity by establishing a relationship between tables

Answer

To prevent duplicate values in a table

Answer

To create a unique index on a column

Answer

To enforce data standardization

Question 18

What is the purpose of an aggregate function in SQL?

Accepted Answer

To perform calculations on groups of data, summarizing information

Answer

To filter data based on a condition

Answer

To create a new table from an existing table

Answer

To update data in a table

Question 19

Which of the following SQL keywords is used to sort the results of a query in ascending or descending order?

Accepted Answer

ORDER BY

Answer

GROUP BY

Answer

HAVING

Answer

WHERE

Question 20

What is the purpose of the 'AUTO_INCREMENT' keyword in SQL?

Accepted Answer

To automatically generate unique, sequential values for a column

Answer

To create a foreign key constraint

Answer

To create a primary key

Answer

To index a column

Question 21

In SQL, which command is used to create a new table?

Accepted Answer

CREATE

Answer

SELECT

Answer

INSERT

Answer

DELETE

Question 22

Which statement best describes the difference between a 'NOT NULL' constraint and a 'UNIQUE' constraint in SQL?

Accepted Answer

'NOT NULL' prevents null values, while 'UNIQUE' ensures that each value is unique.

Answer

'UNIQUE' prevents null values, while 'NOT NULL' ensures that each value is unique.

Answer

'NOT NULL' and 'UNIQUE' are the same constraint.

Question 23

In SQL, which function calculates the average value of a numeric column?

Accepted Answer

AVG()

Answer

COUNT()

Answer

MAX()

Answer

SUM()

Question 24

Which type of 'JOIN' command retrieves only rows with matching values in both tables?

Accepted Answer

INNER JOIN

Answer

LEFT JOIN

Answer

RIGHT JOIN

Answer

FULL JOIN

Question 25

What's the main reason for using the 'GROUP BY' clause in an SQL query?

Accepted Answer

To group rows with the same values and apply aggregate functions to the grouped data.

Answer

To arrange the data in a specific order.

Answer

To eliminate duplicate rows from the results.

Question 26

Which SQL query retrieves customer IDs and the count of orders for customers who have placed more than one order?

Accepted Answer

SELECT customer_id, COUNT(*) AS order_count FROM orders GROUP BY customer_id HAVING order_count > 1;

Answer

SELECT customer_id, SUM(order_count) FROM orders GROUP BY customer_id;

Answer

SELECT * FROM orders WHERE order_count > 1;

Answer

SELECT customer_id FROM orders GROUP BY customer_id;

Question 27

What's the main purpose of using the 'LIMIT' clause in SQL?

Accepted Answer

Restricting the number of rows displayed in the query results

Answer

Arranging the query results in a particular order

Answer

Grouping query results based on similar values

Question 28

Which of the following is NOT a data manipulation command (DML) in SQL?

Accepted Answer

CREATE

Answer

SELECT

Answer

INSERT

Answer

UPDATE

Question 29

What is the correct syntax to create a table named 'Customers' with columns 'id', 'name', and 'city'?

Accepted Answer

CREATE TABLE Customers (id INT, name VARCHAR(255), city VARCHAR(255));

Answer

CREATE Customers (id INT, name VARCHAR(255), city VARCHAR(255));

Answer

Customers CREATE (id INT, name VARCHAR(255), city VARCHAR(255));

Answer

CREATE TABLE (Customers INT, name VARCHAR(255), city VARCHAR(255));

Question 30

Which of the following operators is used to test the equality of two values in SQL?

Accepted Answer

=

Answer

>

Answer

<

Answer

~=

Question 31

What is the purpose of the 'LIMIT' clause in a SQL query?

Accepted Answer

To limit the number of rows returned by the query

Answer

To sort the rows returned by the query

Answer

To group the rows returned by the query

Answer

To delete rows from the table

Question 32

Which aggregate function returns the average value of a column in SQL?

Accepted Answer

AVG()

Answer

SUM()

Answer

COUNT()

Answer

MIN()

Question 33

Explain the difference between a primary key and a foreign key.

Accepted Answer

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

Answer

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

Answer

Both primary keys and foreign keys can be used to uniquely identify rows in a table.

Answer

There is no difference between a primary key and a foreign key.

Question 34

What is the purpose of a JOIN operation in SQL?

Accepted Answer

To combine rows from two or more tables based on a related column

Answer

To update rows in a table

Answer

To delete rows from a table

Answer

To create a new table

Question 35

What is the benefit of using aliases in SQL queries?

Accepted Answer

To give temporary names to tables or columns for easier referencing

Answer

To create new tables

Answer

To update rows in a table

Answer

To delete rows from a table

Question 36

What is the main reason for using the 'INDEX' keyword in SQL?

Accepted Answer

To make data retrieval faster

Answer

To define a primary key

Answer

To create a table

Answer

To remove duplicate data

Question 37

Which data manipulation command is used to retrieve data from a table?

Accepted Answer

SELECT

Answer

INSERT

Answer

UPDATE

Answer

DELETE

Question 38

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

Accepted Answer

To specify conditions for selecting specific rows

Answer

To sort the results of a query

Question 39

What is the difference between an 'INNER JOIN' and an 'OUTER JOIN' in SQL?

Accepted Answer

INNER JOIN returns only matching rows, while OUTER JOIN returns all rows from both tables

Answer

OUTER JOIN returns only matching rows, while INNER JOIN returns all rows from both tables

Question 40

What is the purpose of using a 'GROUP BY' clause in an SQL query?

Accepted Answer

To group the results of the query by one or more columns

Answer

To sort the results of the query

Question 41

Which of the following is NOT a benefit of using a relational database management system (RDBMS)?

Accepted Answer

Increased data complexity

Answer

Improved data security

Question 42

Which of the following SQL statements is used to retrieve data?

Accepted Answer

SELECT * FROM students

Answer

CREATE TABLE students

Answer

ALTER TABLE students ADD COLUMN age

Answer

DROP DATABASE my_database

Question 43

What is the key difference between an 'INNER JOIN' and an 'OUTER JOIN' in SQL?

Accepted Answer

INNER JOIN retains matching rows, while OUTER JOIN retains all rows.

Answer

OUTER JOIN excludes non-matching rows, while INNER JOIN includes all rows.

Answer

INNER JOIN combines matching rows, while OUTER JOIN combines different rows.

Answer

INNER JOIN and OUTER JOIN are identical operations.

Question 44

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

Accepted Answer

To specify conditions and filter rows

Answer

To create a new table

Answer

To update existing data

Answer

To delete rows

Question 45

Which SQL command is used to retrieve specific rows from a table based on a condition?

Accepted Answer

SELECT

Answer

GET

Answer

FETCH

Answer

READ

Question 46

What is a primary purpose of a primary key in a database table?

Accepted Answer

To uniquely identify rows in the table

Answer

To enforce data integrity

Answer

To improve performance

Answer

To store important data

Question 47

Which of the following is a valid example of a data manipulation language (DML) statement in SQL?

Accepted Answer

SELECT

Answer

CREATE TABLE

Answer

DROP DATABASE

Answer

ALTER TABLE

Question 48

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

Accepted Answer

To combine rows from multiple tables based on a shared column

Answer

To create a new table

Answer

To update existing data

Answer

To delete rows

Question 49

Which function can be used to calculate the sum of values in a specified column in SQL?

Accepted Answer

SUM()

Answer

AVG()

Answer

COUNT()

Answer

MIN()

Question 50

What is the difference between a clustered index and a non-clustered index in SQL?

Accepted Answer

Clustered index physically sorts data, while non-clustered index does not

Answer

Non-clustered index physically sorts data, while clustered index does not

Answer

Clustered index is used for primary keys only, while non-clustered index is used for foreign keys only

Answer

Non-clustered index is used for primary keys only, while clustered index is used for foreign keys only