Scalar subqueries in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select the average salary from the employees table.

PostgreSQL

SELECT (SELECT [1](salary) FROM employees) AS avg_salary;

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AAVG

BCOUNT

CSUM

DMAX

Attempts:

3 left

💡 Hint

Common Mistakes

Using SUM instead of AVG returns total salary, not average.

Using COUNT returns number of rows, not average salary.

The AVG function calculates the average value of a column. Here, it returns the average salary.

2fill in blank

medium

Complete the code to find employees whose salary is greater than the average salary.

PostgreSQL

SELECT name FROM employees WHERE salary > (SELECT [1](salary) FROM employees);

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ACOUNT

BSUM

CMIN

DAVG

Attempts:

3 left

💡 Hint

Common Mistakes

Using SUM returns total salary, causing incorrect comparison.

Using MIN returns lowest salary, not average.

The subquery calculates the average salary using AVG. The main query selects employees earning more than this average.

3fill in blank

hard

Fix the error in the scalar subquery to correctly get the maximum salary.

PostgreSQL

SELECT name, salary FROM employees WHERE salary = (SELECT [1](salary) FROM employees);

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AMAX()

BMAX(

CMAX

DMAX)

Attempts:

3 left

💡 Hint

Common Mistakes

Writing MAX without parentheses causes syntax error.

Adding parentheses incorrectly breaks the query.

Use MAX( to form the correct aggregate function syntax MAX(salary) in the scalar subquery.

4fill in blank

hard

Fill both blanks to select employees whose salary is between the minimum and maximum salaries.

PostgreSQL

SELECT name FROM employees WHERE salary BETWEEN (SELECT [1](salary) FROM employees) AND (SELECT [2](salary) FROM employees);

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AMIN

BAVG

CMAX

DSUM

Attempts:

3 left

💡 Hint

Common Mistakes

Using AVG instead of MIN or MAX changes the range incorrectly.

Using SUM does not make sense for range boundaries.

The MIN function gets the lowest salary, and MAX gets the highest. Using BETWEEN with these selects salaries in that range.

5fill in blank

hard

Fill all three blanks to select employees whose salary is greater than the average salary and less than the maximum salary.

PostgreSQL

SELECT name FROM employees WHERE salary > (SELECT [1](salary) FROM employees) AND salary < (SELECT [2](salary) FROM employees) ORDER BY [3];

Drag options to blanks, or click blank then click option'

AMIN

BAVG

CMAX

Dsalary

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up MIN and AVG in comparisons.

Forgetting to order by a valid column.

The query compares salary to the average and maximum using AVG and MAX. It orders results by the salary column.