GROUP BY single and multiple columns in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to group the sales by the product_id.

PostgreSQL

SELECT product_id, SUM(quantity) FROM sales GROUP BY [1];

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

Asales

Bquantity

Cproduct_id

DSUM(quantity)

Attempts:

3 left

💡 Hint

Common Mistakes

Grouping by quantity instead of product_id.

Using aggregate functions in GROUP BY.

We group by product_id to aggregate sales per product.

2fill in blank

medium

Complete the code to group sales by both product_id and store_id.

PostgreSQL

SELECT product_id, store_id, SUM(quantity) FROM sales GROUP BY [1], store_id;

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

Aquantity

Bproduct_id

CSUM(quantity)

Dstore_id

Attempts:

3 left

💡 Hint

Common Mistakes

Grouping by quantity or aggregate functions.

Forgetting to include all selected non-aggregated columns in GROUP BY.

We group by both product_id and store_id to get totals per product per store.

3fill in blank

hard

Fix the error in the GROUP BY clause to correctly group by customer_id.

PostgreSQL

SELECT customer_id, COUNT(*) FROM orders GROUP BY [1];

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

Acustomer_id

BCOUNT(*)

Corders

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Grouping by COUNT(*) which is an aggregate function.

Using table names or * in GROUP BY.

The GROUP BY clause must use the column name customer_id, not an aggregate or table name.

4fill in blank

hard

Fill both blanks to group sales by year and month.

PostgreSQL

SELECT EXTRACT([1] FROM sale_date) AS year, EXTRACT([2] FROM sale_date) AS month, SUM(amount) FROM sales GROUP BY year, month;

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Ayear

Bmonth

Cday

Dquarter

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'day' or 'quarter' instead of 'month'.

Not matching the extracted parts with GROUP BY aliases.

We extract year and month from sale_date to group sales by these periods.

5fill in blank

hard

Fill all three blanks to group employees by department and job title, showing average salary.

PostgreSQL

SELECT [1], [2], AVG(salary) FROM employees GROUP BY [3], job_title;

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

Adepartment

Bjob_title

Dsalary

Attempts:

3 left

💡 Hint

Common Mistakes

Grouping by salary which is aggregated.

Mismatch between SELECT columns and GROUP BY columns.

We select and group by department and job_title to get average salary per group.