UNION and UNION ALL in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to combine results from two tables without duplicates.

PostgreSQL

SELECT name FROM employees [1] SELECT name FROM managers;

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

AUNION

BJOIN

CUNION ALL

DINTERSECT

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNION ALL when duplicates should be removed.

Using JOIN instead of UNION to combine rows.

The UNION keyword combines results from two queries and removes duplicates.

2fill in blank

medium

Complete the code to combine all rows from two tables including duplicates.

PostgreSQL

SELECT product_id FROM sales_2023 [1] SELECT product_id FROM sales_2024;

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

AINTERSECT

BUNION ALL

CUNION

DEXCEPT

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNION instead of UNION ALL when duplicates are needed.

Using INTERSECT which returns only common rows.

The UNION ALL keyword combines all rows from both queries including duplicates.

3fill in blank

hard

Fix the error in the query to combine customer names from two tables.

PostgreSQL

SELECT customer_name FROM customers [1] ALL SELECT customer_name FROM clients;

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

AINTERSECT

BUNION

CJOIN

DUNION ALL

Attempts:

3 left

💡 Hint

Common Mistakes

Writing 'UNION ALL' with extra words or missing space.

Using JOIN instead of UNION ALL.

The correct syntax is UNION ALL without any word between UNION and ALL.

4fill in blank

hard

Fill both blanks to combine two queries and order the results by id.

PostgreSQL

SELECT id FROM table1 [1] SELECT id FROM table2 ORDER BY [2];

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

AUNION

BUNION ALL

Cid

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNION ALL when duplicates should be removed.

Ordering by a column not in the SELECT list.

Use UNION to combine without duplicates and order by id.

5fill in blank

hard

Fill all three blanks to combine two queries selecting user and score, keeping duplicates, and order by score descending.

PostgreSQL

SELECT user, score FROM scores_2022 [1] SELECT user, score FROM scores_2023 ORDER BY [2] [3];

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

AUNION

BUNION ALL

Cscore

DDESC

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNION instead of UNION ALL when duplicates are needed.

Ordering ascending instead of descending.

Use UNION ALL to keep duplicates, order by score in descending order.