SQL Exercises

SQL SELECT Statement Exercises (With Answers)

20 Exercises
~100 min
20 Beginner

Exercise 1

beginner

Question

Write a query to select all columns from the 'employees' table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2),
  department VARCHAR(50),
  hire_date DATE
);
Show Solution

Solution

SQL
1SELECT * FROM employees;

Expected Output

| id | name | salary | department | hire_date |
|---|---|---|---|---|
| 1 | John | 50000 | Sales | 2024-01-15 |

Explanation

The asterisk (*) is a wildcard that selects all columns from the specified table. While convenient for exploration, in production code it's better to explicitly list column names.

Exercise 1

beginner

Question

Write a query to select all columns from the 'employees' table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2),
  department VARCHAR(50),
  hire_date DATE
);
Show Solution

Solution

SQL
1SELECT * FROM employees;

Expected Output

| id | name | salary | department | hire_date |
|---|---|---|---|---|
| 1 | John | 50000 | Sales | 2024-01-15 |

Explanation

The asterisk (*) is a wildcard that selects all columns from the specified table. While convenient for exploration, in production code it's better to explicitly list column names.

Exercise 1

beginner

Question

Write a query to select all columns from the 'employees' table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2),
  department VARCHAR(50),
  hire_date DATE
);
Show Solution

Solution

SQL
1SELECT * FROM employees;

Expected Output

| id | name | salary | department | hire_date |
|---|---|---|---|---|
| 1 | John | 50000 | Sales | 2024-01-15 |

Explanation

The asterisk (*) is a wildcard that selects all columns from the specified table. While convenient for exploration, in production code it's better to explicitly list column names.

Exercise 1

beginner

Question

Write a query to select all columns from the 'employees' table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2),
  department VARCHAR(50),
  hire_date DATE
);
Show Solution

Solution

SQL
1SELECT * FROM employees;

Expected Output

| id | name | salary | department | hire_date |
|---|---|---|---|---|
| 1 | John | 50000 | Sales | 2024-01-15 |

Explanation

The asterisk (*) is a wildcard that selects all columns from the specified table. While convenient for exploration, in production code it's better to explicitly list column names.

Exercise 2

beginner

Question

Select only the 'name' and 'salary' columns from the 'employees' table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2),
  department VARCHAR(50)
);
Show Solution

Solution

SQL
1SELECT name, salary FROM employees;

Expected Output

| name | salary |
|---|---|
| John | 50000 |
| Jane | 60000 |

Explanation

Explicitly listing column names is a best practice. It improves query performance and makes your code more maintainable.

Exercise 2

beginner

Question

Select only the 'name' and 'salary' columns from the 'employees' table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2),
  department VARCHAR(50)
);
Show Solution

Solution

SQL
1SELECT name, salary FROM employees;

Expected Output

| name | salary |
|---|---|
| John | 50000 |
| Jane | 60000 |

Explanation

Explicitly listing column names is a best practice. It improves query performance and makes your code more maintainable.

Exercise 2

beginner

Question

Select only the 'name' and 'salary' columns from the 'employees' table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2),
  department VARCHAR(50)
);
Show Solution

Solution

SQL
1SELECT name, salary FROM employees;

Expected Output

| name | salary |
|---|---|
| John | 50000 |
| Jane | 60000 |

Explanation

Explicitly listing column names is a best practice. It improves query performance and makes your code more maintainable.

Exercise 2

beginner

Question

Select only the 'name' and 'salary' columns from the 'employees' table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2),
  department VARCHAR(50)
);
Show Solution

Solution

SQL
1SELECT name, salary FROM employees;

Expected Output

| name | salary |
|---|---|
| John | 50000 |
| Jane | 60000 |

Explanation

Explicitly listing column names is a best practice. It improves query performance and makes your code more maintainable.

Exercise 3

beginner

Question

Select all employees and add a calculated column showing annual bonus (10% of salary).

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2)
);
Show Solution

Solution

SQL
1SELECT name, salary, salary * 0.10 AS annual_bonus FROM employees;

Expected Output

| name | salary | annual_bonus |
|---|---|---|
| John | 50000 | 5000 |

Explanation

You can perform calculations in the SELECT clause and use AS to create an alias for the calculated column.

Exercise 3

beginner

Question

Select all employees and add a calculated column showing annual bonus (10% of salary).

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2)
);
Show Solution

Solution

SQL
1SELECT name, salary, salary * 0.10 AS annual_bonus FROM employees;

Expected Output

| name | salary | annual_bonus |
|---|---|---|
| John | 50000 | 5000 |

Explanation

You can perform calculations in the SELECT clause and use AS to create an alias for the calculated column.

Exercise 3

beginner

Question

Select all employees and add a calculated column showing annual bonus (10% of salary).

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2)
);
Show Solution

Solution

SQL
1SELECT name, salary, salary * 0.10 AS annual_bonus FROM employees;

Expected Output

| name | salary | annual_bonus |
|---|---|---|
| John | 50000 | 5000 |

Explanation

You can perform calculations in the SELECT clause and use AS to create an alias for the calculated column.

Exercise 3

beginner

Question

Select all employees and add a calculated column showing annual bonus (10% of salary).

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2)
);
Show Solution

Solution

SQL
1SELECT name, salary, salary * 0.10 AS annual_bonus FROM employees;

Expected Output

| name | salary | annual_bonus |
|---|---|---|
| John | 50000 | 5000 |

Explanation

You can perform calculations in the SELECT clause and use AS to create an alias for the calculated column.

Exercise 4

beginner

Question

Select unique department names from the employees table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  department VARCHAR(50)
);
Show Solution

Solution

SQL
1SELECT DISTINCT department FROM employees;

Expected Output

| department |
|---|
| Sales |
| Engineering |
| Marketing |

Explanation

DISTINCT removes duplicate values from the result set. It's useful for finding unique values in a column.

Exercise 4

beginner

Question

Select unique department names from the employees table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  department VARCHAR(50)
);
Show Solution

Solution

SQL
1SELECT DISTINCT department FROM employees;

Expected Output

| department |
|---|
| Sales |
| Engineering |
| Marketing |

Explanation

DISTINCT removes duplicate values from the result set. It's useful for finding unique values in a column.

Exercise 4

beginner

Question

Select unique department names from the employees table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  department VARCHAR(50)
);
Show Solution

Solution

SQL
1SELECT DISTINCT department FROM employees;

Expected Output

| department |
|---|
| Sales |
| Engineering |
| Marketing |

Explanation

DISTINCT removes duplicate values from the result set. It's useful for finding unique values in a column.

Exercise 4

beginner

Question

Select unique department names from the employees table.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  department VARCHAR(50)
);
Show Solution

Solution

SQL
1SELECT DISTINCT department FROM employees;

Expected Output

| department |
|---|
| Sales |
| Engineering |
| Marketing |

Explanation

DISTINCT removes duplicate values from the result set. It's useful for finding unique values in a column.

Exercise 5

beginner

Question

Select the first 5 employees ordered by salary descending.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2)
);
Show Solution

Solution

SQL
1SELECT * FROM employees ORDER BY salary DESC LIMIT 5;

Expected Output

| id | name | salary |
|---|---|---|
| 3 | Alice | 75000 |
| 2 | Bob | 65000 |

Explanation

ORDER BY sorts results (DESC for descending). LIMIT restricts the number of rows returned. This pattern is common for 'top N' queries.

Exercise 5

beginner

Question

Select the first 5 employees ordered by salary descending.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2)
);
Show Solution

Solution

SQL
1SELECT * FROM employees ORDER BY salary DESC LIMIT 5;

Expected Output

| id | name | salary |
|---|---|---|
| 3 | Alice | 75000 |
| 2 | Bob | 65000 |

Explanation

ORDER BY sorts results (DESC for descending). LIMIT restricts the number of rows returned. This pattern is common for 'top N' queries.

Exercise 5

beginner

Question

Select the first 5 employees ordered by salary descending.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2)
);
Show Solution

Solution

SQL
1SELECT * FROM employees ORDER BY salary DESC LIMIT 5;

Expected Output

| id | name | salary |
|---|---|---|
| 3 | Alice | 75000 |
| 2 | Bob | 65000 |

Explanation

ORDER BY sorts results (DESC for descending). LIMIT restricts the number of rows returned. This pattern is common for 'top N' queries.

Exercise 5

beginner

Question

Select the first 5 employees ordered by salary descending.

Table Schema

SQL
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary DECIMAL(10,2)
);
Show Solution

Solution

SQL
1SELECT * FROM employees ORDER BY salary DESC LIMIT 5;

Expected Output

| id | name | salary |
|---|---|---|
| 3 | Alice | 75000 |
| 2 | Bob | 65000 |

Explanation

ORDER BY sorts results (DESC for descending). LIMIT restricts the number of rows returned. This pattern is common for 'top N' queries.

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