COUNT function in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to count all rows in the employees table.

MySQL

SELECT [1](*) FROM employees;

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

ATOTAL

BSUM

CCOUNT

DNUMBER

Attempts:

3 left

💡 Hint

Common Mistakes

Using SUM instead of COUNT.

Using TOTAL or NUMBER which are not valid SQL functions.

The COUNT function counts the number of rows. Using COUNT(*) counts all rows in the table.

2fill in blank

medium

Complete the code to count only the non-null values in the salary column.

MySQL

SELECT COUNT([1]) FROM employees;

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Asalary

BDISTINCT salary

CNULL

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using COUNT(*) which counts all rows regardless of nulls.

Using COUNT(NULL) which always returns zero.

COUNT(column) counts only non-null values in that column. Here, COUNT(salary) counts all employees with a salary value.

3fill in blank

hard

Fix the error in the code to count distinct departments.

MySQL

SELECT COUNT([1] department) FROM employees;

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ASINGLE

BALL

CUNIQUE

DDISTINCT

Attempts:

3 left

💡 Hint

Common Mistakes

Using ALL which counts all values including duplicates.

Using UNIQUE or SINGLE which are not valid SQL keywords here.

COUNT(DISTINCT column) counts unique non-null values in that column. DISTINCT is the correct keyword.

4fill in blank

hard

Fill both blanks to count employees with salary greater than 50000.

MySQL

SELECT COUNT([1]) FROM employees WHERE salary [2] 50000;

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A*

Bsalary

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using COUNT(salary) which counts only non-null salaries but is less clear here.

Using < instead of > which counts salaries less than 50000.

COUNT(*) counts all rows matching the condition. The condition salary > 50000 filters employees with salary above 50000.

5fill in blank

hard

Fill all three blanks to count distinct job titles with salary less than 70000.

MySQL

SELECT COUNT([1] job_title) FROM employees WHERE salary [2] [3];

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ADISTINCT

B<

C70000

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using > instead of < which counts salaries greater than 70000.

Not using DISTINCT which counts duplicates.

COUNT(DISTINCT job_title) counts unique job titles. The condition salary < 70000 filters employees with salary less than 70000.