Why server-side programming matters in PostgreSQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from the users table.

PostgreSQL

SELECT [1] FROM users;

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

A*

Ball

Ceverything

Dcolumns

Attempts:

3 left

💡 Hint

Common Mistakes

Using words like 'all' or 'columns' instead of the symbol *.

Leaving the SELECT statement incomplete.

The asterisk (*) means select all columns from the table.

2fill in blank

medium

Complete the code to filter users with age greater than 18.

PostgreSQL

SELECT * FROM users WHERE age [1] 18;

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

A<

B<=

C=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' which means less than.

Using '=' which means equal to.

The '>' operator filters for ages greater than 18.

3fill in blank

hard

Fix the error in the query to count users by country.

PostgreSQL

SELECT country, COUNT([1]) FROM users GROUP BY country;

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

Auser_id

B*

Ccountry

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Counting a specific column that might have nulls, leading to wrong counts.

Using the grouping column inside COUNT which is not typical.

Using COUNT(*) counts all rows per country, which is correct here.

4fill in blank

hard

Fill both blanks to select names and ages of users older than 25.

PostgreSQL

SELECT [1], [2] FROM users WHERE age > 25;

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

Aname

Bage

Ccountry

Demail

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting unrelated columns like 'country' or 'email'.

Selecting only one column instead of both.

We select 'name' and 'age' columns to see users' names and ages.

5fill in blank

hard

Fill all three blanks to create a dictionary of user emails and their countries for users older than 30.

PostgreSQL

SELECT [1], [2] FROM users WHERE age [3] 30;

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

Aemail

Bcountry

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' for age comparison.

Selecting wrong columns like 'name' or 'age' instead of 'email' and 'country'.

Select 'email' and 'country' columns and filter users with age greater than 30.