MySQL vs PostgreSQL vs SQL Server overview - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from a table named 'employees'.

SQL

SELECT [1] FROM employees;

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

AALL

B*

CEVERY

DCOLUMNS

Attempts:

3 left

💡 Hint

Common Mistakes

Using keywords like ALL or COLUMNS which are not valid in this context.

Trying to write column names instead of using the wildcard.

In SQL, * means select all columns from the table.

2fill in blank

medium

Complete the code to filter rows where the 'age' column is greater than 30.

SQL

SELECT * FROM users WHERE age [1] 30;

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

A<

B<=

C=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' which filters the wrong rows.

Using '=' which only matches exactly 30.

The symbol > means 'greater than' in SQL conditions.

3fill in blank

hard

Fix the error in the SQL query to count the number of rows in the 'orders' table.

SQL

SELECT COUNT([1]) FROM orders;

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

A*

Border_id

Call

Drows

Attempts:

3 left

💡 Hint

Common Mistakes

Using COUNT(all) or COUNT(rows) which are invalid.

Using COUNT(column) which may miss rows with NULL in that column.

Using COUNT(*) counts all rows regardless of NULLs.

4fill in blank

hard

Fill both blanks to create a query that selects the 'name' and 'salary' columns from 'employees' where salary is at least 50000.

SQL

SELECT [1], [2] FROM employees WHERE salary [3] 50000;

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

Aname

Bsalary

C>=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>=' which filters wrong rows.

Selecting wrong column names.

Select name and salary columns, and filter salaries greater than or equal to 50000 using >=.

5fill in blank

hard

Fill all three blanks to create a query that counts how many employees have a department ID less than 10.

SQL

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

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

A*

B<

C10

Ddepartment_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using COUNT(department_id) which misses NULLs.

Using wrong comparison operators or values.

Use COUNT(*) to count all rows, filter where department_id < 10.