Why result control matters in PostgreSQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

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

PostgreSQL

SELECT [1] FROM employees;

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AALL_COLUMNS

BALL

CANY

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using ALL or ANY instead of *

Trying to write ALL_COLUMNS which is not valid SQL

The asterisk (*) selects all columns from the table.

2fill in blank

medium

Complete the code to get only unique department names from the departments table.

PostgreSQL

SELECT [1] department_name FROM departments;

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ADISTINCT

BUNIQUE

CSINGLE

DONLY

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNIQUE which is not a valid SQL keyword here

Using ONLY which is not a SQL keyword

DISTINCT returns unique values, removing duplicates.

3fill in blank

hard

Fix the error in the query to order employees by salary descending.

PostgreSQL

SELECT * FROM employees ORDER BY salary [1];

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AASC

BDOWN

CDESC

DBACK

Attempts:

3 left

💡 Hint

Common Mistakes

Using ASC which orders ascending

Using DOWN or BACK which are not valid SQL keywords

DESC orders results from highest to lowest.

4fill in blank

hard

Fill both blanks to select employee names and salaries where salary is greater than 50000.

PostgreSQL

SELECT employee_name, salary FROM employees WHERE salary [1] [2];

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A>

B50000

C<

D100000

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than operator < instead of >

Using 100000 instead of 50000

The WHERE clause filters salaries greater than 50000 using > 50000.

5fill in blank

hard

Fill all three blanks to create a query that selects department names and counts employees, grouping by department and showing only groups with more than 5 employees.

PostgreSQL

SELECT [1], COUNT(*) FROM employees GROUP BY [2] HAVING COUNT(*) [3] 5;

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

Adepartment_name

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using different columns in SELECT and GROUP BY

Using less than operator < in HAVING clause

We select and group by department_name, then use HAVING with > 5 to filter groups with more than 5 employees.