SQL Foundations

Question 1

What does SQL stand for?

Answer 1

Structured Query Language

Question 2

What is a database?

Answer 2

An organized collection of data stored and accessed electronically

Question 3

What SQL command is used to retrieve data?

Answer 3

SELECT

Question 4

What SQL keyword is used to remove duplicate values?

Answer 4

DISTINCT

Question 5

How do you select all columns from a table named employees?

Answer 5

SELECT * FROM employees;

Question 6

What SQL clause filters rows based on a condition?

Answer 6

WHERE

Question 7

How do you retrieve employees with a salary greater than 50000?

Answer 7

SELECT * FROM employees WHERE salary > 50000;

Question 8

What is the purpose of the ORDER BY clause?

Answer 8

To sort the results by one or more columns

Question 9

How do you sort results by name in descending order?

Answer 9

ORDER BY name DESC

Question 10

What is the default sort order for ORDER BY?

Answer 10

Ascending (ASC)

Question 11

What clause is used to group rows that have the same values?

Answer 11

GROUP BY

Question 12

How do you find the number of employees in each department?

Answer 12

SELECT department

Question 13

What function calculates the number of rows?

Answer 13

COUNT()

Question 14

What function returns the average value of a column?

Answer 14

AVG()

Question 15

What function returns the largest value?

Answer 15

MAX()

Question 16

What function returns the smallest value?

Answer 16

MIN()

Question 17

What function returns the sum of values in a column?

Answer 17

SUM()

Question 18

What SQL clause filters groups created by GROUP BY?

Answer 18

HAVING

Question 19

What is the difference between WHERE and HAVING?

Answer 19

WHERE filters rows before grouping; HAVING filters groups after grouping

Question 20

What SQL statement is used to insert data?

Answer 20

INSERT INTO

Question 21

How do you insert a row into a table?

Answer 21

INSERT INTO table_name (column1

Question 22

What statement modifies existing data?

Answer 22

UPDATE

Question 23

How do you update the salary of an employee with ID 3?

Answer 23

UPDATE employees SET salary = new_value WHERE id = 3;

Question 24

What command deletes rows from a table?

Answer 24

DELETE

Question 25

How do you delete all employees in department 10?

Answer 25

DELETE FROM employees WHERE department = 10;

Question 26

How do you delete all records from a table but keep its structure?

Answer 26

DELETE FROM table_name;

Question 27

How do you remove a table and its structure?

Answer 27

DROP TABLE table_name;

Question 28

What command creates a new table?

Answer 28

CREATE TABLE

Question 29

What SQL clause defines the data type and constraints of a column?

Answer 29

CREATE TABLE column definitions

Question 30

What is a primary key?

Answer 30

A column or set of columns that uniquely identifies each row in a table

Question 31

How do you define a primary key in SQL?

Answer 31

CREATE TABLE example (id INT PRIMARY KEY

Question 32

What is a foreign key?

Answer 32

A column that refers to the primary key in another table

Question 33

How do you join two tables?

Answer 33

Using JOIN with a matching condition

Question 34

What does INNER JOIN do?

Answer 34

Returns only rows with matching keys in both tables

Question 35

What does LEFT JOIN do?

Answer 35

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

Question 36

What does RIGHT JOIN do?

Answer 36

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

Question 37

What does FULL OUTER JOIN do?

Answer 37

Returns all rows from both tables with NULLs for missing matches

Question 38

What does NULL mean in SQL?

Answer 38

A missing or unknown value

Question 39

How do you check for NULL values?

Answer 39

Use IS NULL or IS NOT NULL

Question 40

How do you rename a column in the result?

Answer 40

Use AS: SELECT name AS employee_name FROM employees;

Question 41

What clause limits the number of returned rows?

Answer 41

LIMIT