SQL Learning Quizzes: Master Relational Database Management

Question 1

To optimize the performance of the following SQL query, which strategy would be most effective?

```
SELECT * FROM orders WHERE customer_id = 12345
```

Accepted Answer

Create an index on the customer_id column

Answer

Replace the WHERE = clause with a WHERE IN clause

Answer

Increase the size of the buffer pool

Question 2

In SQL, how do primary and foreign keys contribute to data integrity in relational databases?

Accepted Answer

They enforce referential integrity, preventing orphaned records and maintaining data relationships.

Answer

They ensure data accuracy by preventing duplicate values across tables.

Answer

They optimize query performance by facilitating efficient table joins.

Answer

They simplify data entry by auto-generating unique identifiers for each table row.

Question 3

In SQL, an INNER JOIN combines rows from two tables based on a matching column. Which statement accurately describes the behavior of an INNER JOIN?

Accepted Answer

Returns all rows from the left table and only matching rows from the right table.

Answer

Returns all rows from both tables, regardless of matching values.

Answer

Returns all rows from the right table and only matching rows from the left table.

Answer

Returns only rows without matching values in either table.

Question 4

Which data type in SQL stores whole numbers?

Accepted Answer

INT

Answer

CHAR

Answer

VARCHAR

Answer

DATE

Question 5

In SQL, what is the primary purpose of the 'SELECT' statement?

Accepted Answer

Retrieve data from a table

Answer

Create a new table

Answer

Update data in a table

Answer

Delete data from a table

Question 6

Which operator in SQL is used to check if two values are equal?

Accepted Answer

=

Answer

!=

Answer

>

Answer

<

Question 7

What is the key difference between a primary key and a foreign key in a relational database?

Accepted Answer

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

Answer

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

Answer

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

Answer

Both primary keys and foreign keys are used to create relationships between tables.

Question 8

Which of the following is NOT considered a Data Manipulation Language (DML) statement in SQL?

Accepted Answer

SELECT

Answer

INSERT

Answer

UPDATE

Answer

DELETE

Question 9

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

Accepted Answer

Filter the data based on specific conditions

Answer

Specify the columns to be retrieved

Answer

Sort the data in a particular order

Answer

Group the data by a specified column

Question 10

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

Accepted Answer

Combine rows from multiple tables based on a common column

Answer

Update data in multiple tables simultaneously

Answer

Delete data from multiple tables simultaneously

Answer

Create a new table from the results of a query

Question 11

What is the main advantage of using an index in an SQL database?

Accepted Answer

Enhances the speed of queries by optimizing data retrieval

Answer

Ensures data consistency and integrity

Answer

Prevents duplicate data entry

Answer

Provides enhanced data security

Question 12

Which SQL data type is specifically designed to store dates and times?

Accepted Answer

DATE

Accepted Answer

TIMESTAMP

Answer

INT

Answer

VARCHAR

Question 13

In SQL, which data type is suitable for storing whole numbers without decimal places?

Accepted Answer

INTEGER

Answer

FLOAT

Answer

DOUBLE

Answer

TEXT

Question 14

Which SQL statement is used to create a new database table?

Accepted Answer

CREATE TABLE

Answer

DROP TABLE

Answer

SELECT * FROM

Answer

INSERT INTO

Question 15

In SQL, which operator is used to compare the equality of two values?

Accepted Answer

=

Answer

==

Answer

<>

Answer

IS NOT

Question 16

Which clause in SQL is used to restrict the rows returned by a query based on specified conditions?

Accepted Answer

WHERE

Answer

ORDER BY

Answer

GROUP BY

Answer

LIMIT

Question 17

In SQL, which function is used to calculate the average value of a set of numbers?

Accepted Answer

AVG

Answer

SUM

Answer

MIN

Answer

MAX

Question 18

Which join type in SQL returns all rows from the left table and only the matching rows from the right table?

Accepted Answer

LEFT JOIN

Answer

INNER JOIN

Answer

RIGHT JOIN

Answer

FULL JOIN

Question 19

Which SQL statement is used to remove rows from a table?

Accepted Answer

DELETE FROM

Answer

UPDATE

Answer

INSERT INTO

Answer

DROP TABLE

Question 20

In SQL, which type of key ensures that each row in a table has a unique value?

Accepted Answer

Primary key

Answer

Foreign key

Answer

Unique key

Answer

Candidate key

Question 21

Which indexing technique in SQL speeds up query execution by creating a data structure that maps values to their corresponding row locations?

Accepted Answer

B-tree

Answer

Hashing

Answer

Linear search

Answer

Binary search

Question 22

In SQL, which statement is used to retrieve data from a database?

Accepted Answer

SELECT

Answer

INSERT

Answer

UPDATE

Answer

DELETE

Question 23

Which keyword in SQL is used to create a new table?

Accepted Answer

CREATE

Answer

TABLE

Answer

INSERT

Answer

SELECT

Question 24

In an SQL query, which clause allows you to filter and select specific rows based on conditions?

Accepted Answer

WHERE

Answer

ORDER BY

Answer

GROUP BY

Answer

HAVING

Question 25

What is the primary purpose of using an SQL JOIN?

Accepted Answer

To merge rows from multiple tables based on matching values

Answer

To create a new table

Answer

To delete rows from a table

Answer

To update rows in a table

Question 26

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

Accepted Answer

AVG

Answer

COUNT

Answer

SUM

Answer

MAX

Question 27

What is the primary function of a foreign key constraint in SQL?

Accepted Answer

To maintain referential integrity by ensuring data consistency between related tables

Answer

To enforce uniqueness of data within a table

Answer

To create a primary key for a table

Answer

To set default values for columns

Question 28

Which SQL command is used to modify and update existing rows in a table?

Accepted Answer

UPDATE

Answer

INSERT

Answer

DELETE

Answer

SELECT

Question 29

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

Accepted Answer

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

Answer

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

Answer

Primary keys and foreign keys serve identical purposes in SQL

Answer

Foreign keys can be nullable, but primary keys cannot

Question 30

What is the main purpose of using an SQL transaction?

Accepted Answer

To group multiple SQL statements into a single logical unit of work

Answer

To create a backup of an entire database

Answer

To permanently remove all data from a table

Answer

To improve the performance of individual SQL queries

Question 31

In the 'orders' and 'customers' tables, write an SQL query that displays each customer's name and the total number of orders they've placed.

Accepted Answer

SELECT customer_name, COUNT(*) AS order_count FROM orders GROUP BY customer_id

Answer

SELECT * FROM orders JOIN customers ON orders.customer_id = customers.customer_id

Answer

SELECT customer_name, SUM(order_id) AS order_count FROM orders GROUP BY customer_id

Question 32

Which SQL query retrieves the names of customers who have placed multiple orders?

Accepted Answer

SELECT CustomerName FROM Orders GROUP BY CustomerName HAVING COUNT(*) > 1;

Answer

SELECT COUNT(*) FROM Customers WHERE OrderID > 1;

Answer

SELECT DISTINCT CustomerName FROM Orders WHERE OrderID > 1;

Question 33

Which SQL statement adds a column named 'discount' with a data type of 'decimal' to the table 'orders'?

Accepted Answer

ALTER TABLE orders ADD COLUMN discount decimal;

Answer

UPDATE orders SET discount = 0.10;

Answer

CREATE COLUMN discount decimal IN orders;

Answer

ADD COLUMN discount decimal TO orders;

Question 34

Which of these is NOT a standard SQL data type?

Accepted Answer

ARRAY

Answer

INTEGER

Answer

VARCHAR

Answer

BOOLEAN

Question 35

Which SQL command is used to create a new database table?

Accepted Answer

CREATE TABLE

Answer

SELECT *

Answer

INSERT INTO

Question 36

Which operator is used for logical 'AND' in SQL?

Accepted Answer

AND

Answer

|

Answer

&

Answer

OR

Question 37

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

Accepted Answer

To filter rows based on a specified condition

Answer

To sort rows in ascending order

Answer

To limit the number of rows returned

Answer

To create a new table

Question 38

Which of the following is NOT a primary function of a SQL database management system?

Accepted Answer

Data compression

Answer

Data retrieval

Answer

Data manipulation

Answer

Data storage

Question 39

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

Accepted Answer

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

Answer

A primary key is always an integer, while a foreign key can be any data type.

Question 40

Which SQL command is used to modify data within a table?

Accepted Answer

UPDATE

Answer

SELECT

Answer

INSERT INTO

Answer

DELETE

Question 41

What is the primary purpose of an SQL index?

Accepted Answer

To enhance the speed of query execution

Answer

To create a backup of the database

Answer

To store frequently accessed data

Answer

To enforce data integrity

Question 42

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

Accepted Answer

SELECT

Answer

DELETE

Answer

CREATE

Answer

UPDATE

Question 43

What is the main purpose of the 'JOIN' keyword in SQL?

Accepted Answer

To combine rows from multiple tables based on a common value

Answer

To filter rows based on a condition

Answer

To create a new table

Question 44

Which SQL statement is used to define a new table with a name and set of columns?

Accepted Answer

CREATE TABLE table_name (column1 data_type, column2 data_type, ...);

Answer

NEW TABLE table_name (column1 data_type, column2 data_type, ...);

Answer

BUILD TABLE table_name (column1 data_type, column2 data_type, ...);

Answer

MAKE TABLE table_name (column1 data_type, column2 data_type, ...);

Question 45

What is the primary purpose of specifying a PRIMARY KEY constraint on a column in an SQL table?

Accepted Answer

To ensure that each row in the table has a unique value for that column

Answer

To speed up data retrieval queries

Answer

To enforce referential integrity with other tables

Answer

To prevent null values from being inserted into the column

Question 46

What is the result of executing the following SQL statement: SELECT * FROM customers WHERE age > 25;

Accepted Answer

Retrieves all rows from the 'customers' table where the 'age' column is greater than 25

Answer

Updates the 'age' column of all customers older than 25 to be 25

Answer

Counts the number of customers in the 'customers' table who are older than 25

Question 47

Which SQL statement is used to add a new row of data to a table?

Accepted Answer

INSERT INTO table_name (column1, column2, ...) VALUES (value1, value2, ...);

Answer

APPEND INTO table_name (column1, column2, ...) VALUES (value1, value2, ...);

Answer

UPDATE table_name SET column1 = value1, column2 = value2, ... WHERE ...;

Answer

ADD ROW TO table_name (column1, column2, ...) VALUES (value1, value2, ...);

Question 48

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

Accepted Answer

An INNER JOIN only includes rows that have matching values in both tables, while an OUTER JOIN includes all rows from one table and any matching rows from the other table

Answer

An INNER JOIN is used to combine rows from two tables based on a common column, while an OUTER JOIN is used to combine rows from two tables based on different columns

Answer

An INNER JOIN always returns fewer rows than an OUTER JOIN

Question 49

Which SQL function is used to calculate the highest value in a set of values?

Accepted Answer

MAX(column_name)

Answer

AVG(column_name)

Answer

SUM(column_name)

Answer

MIN(column_name)

Question 50

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

Accepted Answer

To filter the rows returned by the query based on specified conditions

Answer

To sort the rows returned by the query

Answer

To group the rows returned by the query

Answer

To limit the number of rows returned by the query

Question 51

Which SQL command is used to make changes to the database permanent after a series of operations?

Accepted Answer

COMMIT

Answer

PERSIST

Answer

SAVE

Answer

FINALIZE