GROUPING SETS for multiple groupings in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select the total sales grouped by region and product using GROUPING SETS.

PostgreSQL

SELECT region, product, SUM(sales) FROM sales_data GROUP BY [1];

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

AGROUPING SETS ((region), (product))

Bregion, product

CROLLUP (region, product)

DCUBE (region, product)

Attempts:

3 left

💡 Hint

Common Mistakes

Using just column names without GROUPING SETS.

Using ROLLUP or CUBE which group differently.

The GROUPING SETS clause allows grouping by multiple sets of columns separately. Here, grouping by region and product individually is done by GROUPING SETS ((region), (product)).

2fill in blank

medium

Complete the code to group sales by region and product, and also by region alone using GROUPING SETS.

PostgreSQL

SELECT region, product, SUM(sales) FROM sales_data GROUP BY [1];

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

AGROUPING SETS ((region, product), (region))

BGROUPING SETS ((region), (product))

CROLLUP (region, product)

DGROUP BY region, product

Attempts:

3 left

💡 Hint

Common Mistakes

Using ROLLUP which adds subtotals but not exactly these groupings.

Using GROUP BY with columns directly without GROUPING SETS.

This GROUPING SETS clause groups by both (region, product) and (region) separately, giving totals per product per region and totals per region.

3fill in blank

hard

Fix the error in the GROUP BY clause to correctly use GROUPING SETS for grouping by product and year.

PostgreSQL

SELECT product, year, SUM(amount) FROM sales GROUP BY [1];

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

AGROUPING SETS ((product, year))

BGROUP BY product, year

CGROUPING SETS (product, year)

DGROUPING SETS ((product), (year))

Attempts:

3 left

💡 Hint

Common Mistakes

Not using parentheses around each grouping set.

Using GROUP BY without GROUPING SETS for multiple groupings.

GROUPING SETS requires each grouping set to be enclosed in parentheses. So to group by product and year separately, use GROUPING SETS ((product), (year)).

4fill in blank

hard

Fill both blanks to group sales by region and product, and also by product alone using GROUPING SETS.

PostgreSQL

SELECT region, product, SUM(sales) FROM sales_data GROUP BY [1], [2];

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

AGROUPING SETS ((region, product), (product))

BROLLUP (region, product)

CGROUP BY region, product

DCUBE (region, product)

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to put multiple grouping clauses separated by commas.

Using ROLLUP or CUBE instead of GROUPING SETS.

GROUPING SETS can be used in the GROUP BY clause as a single argument. Here, both blanks should be filled with the same GROUPING SETS clause to form a valid GROUP BY.

5fill in blank

hard

Fill all three blanks to select region, product, and year with total sales grouped by these combinations using GROUPING SETS.

PostgreSQL

SELECT [1], [2], [3], SUM(sales) FROM sales_data GROUP BY GROUPING SETS ((region, product), (region, year), (product, year));

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

Aregion

Bproduct

Cyear

Dsales

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting the aggregated column without SUM or other aggregation.

Missing one of the grouping columns in SELECT.

The SELECT clause must list the columns used in the GROUPING SETS: region, product, and year. The sales column is aggregated, so it is not selected directly.

Practice

1. What is the main purpose of using GROUPING SETS in a PostgreSQL query?

easy

A. To group data by multiple combinations in a single query

B. To filter rows based on conditions

C. To join multiple tables together

D. To sort the result set by multiple columns

Solution

1. Step 1: Understand GROUPING SETS functionality

   GROUPING SETS allows grouping by multiple sets of columns in one query, combining results.

2. Step 2: Compare with other options

   Filtering rows is done by WHERE, joining tables by JOIN, sorting by ORDER BY, not GROUPING SETS.

3. Final Answer:

   To group data by multiple combinations in a single query -> Option A

4. Quick Check:

   GROUPING SETS = multiple groupings in one query [OK]

Hint: GROUPING SETS groups multiple ways at once [OK]

Common Mistakes:

• Confusing GROUPING SETS with WHERE filtering
• Thinking GROUPING SETS sorts data
• Mixing GROUPING SETS with JOIN operations

2. Which of the following is the correct syntax to use GROUPING SETS in a PostgreSQL query?

easy

A. SELECT col1, col2 FROM table ORDER BY GROUPING SETS (col1, col2);

B. SELECT col1, col2 FROM table WHERE GROUPING SETS (col1, col2);

C. SELECT col1, col2 FROM table HAVING GROUPING SETS (col1, col2);

D. SELECT col1, col2 FROM table GROUP BY GROUPING SETS ((col1), (col2));

Solution

1. Step 1: Identify correct GROUP BY usage

   GROUPING SETS is used inside GROUP BY clause with sets of columns in parentheses.

2. Step 2: Check other clauses

   WHERE, ORDER BY, HAVING do not support GROUPING SETS syntax.

3. Final Answer:

   SELECT col1, col2 FROM table GROUP BY GROUPING SETS ((col1), (col2)); -> Option D

4. Quick Check:

   GROUPING SETS goes inside GROUP BY [OK]

Hint: GROUPING SETS always follows GROUP BY keyword [OK]

Common Mistakes:

• Placing GROUPING SETS in WHERE clause
• Using GROUPING SETS with ORDER BY
• Confusing HAVING with GROUP BY for GROUPING SETS

3. Given the table sales(product, region, amount), what will be the output of this query?

SELECT product, region, SUM(amount) FROM sales GROUP BY GROUPING SETS ((product), (region));

medium

A. Sum of amounts grouped by product only

B. Sum of amounts grouped by product and region combined

C. Sum of amounts grouped by product and sum grouped by region in one result

D. Syntax error due to wrong GROUPING SETS usage

Solution

1. Step 1: Understand GROUPING SETS ((product), (region))

   This groups data twice: once by product alone, once by region alone, producing two sets of grouped sums.

2. Step 2: Analyze output rows

   Result will have rows with product and NULL region, and rows with region and NULL product, each showing sum of amounts.

3. Final Answer:

   Sum of amounts grouped by product and sum grouped by region in one result -> Option C

4. Quick Check:

   GROUPING SETS gives multiple groupings combined [OK]

Hint: GROUPING SETS returns all specified groupings combined [OK]

Common Mistakes:

• Expecting grouping by both columns together
• Thinking it returns only one grouping
• Assuming syntax error without checking GROUP BY clause

4. Identify the error in this query:

SELECT product, region, SUM(amount) FROM sales GROUP BY GROUPING SETS (product, region);

medium

A. Missing WHERE clause for filtering

B. GROUPING SETS requires each grouping to be enclosed in parentheses

C. GROUP BY cannot have multiple columns

D. SUM() cannot be used with GROUPING SETS

Solution

1. Step 1: Check GROUPING SETS syntax

   GROUPING SETS expects a list of grouping sets, each enclosed in parentheses, e.g., ((product), (region)).

2. Step 2: Identify the error

   The query uses (product, region) without extra parentheses, which is invalid syntax for GROUPING SETS.

3. Final Answer:

   GROUPING SETS requires each grouping to be enclosed in parentheses -> Option B

4. Quick Check:

   GROUPING SETS syntax needs nested parentheses [OK]

Hint: Each grouping set must be in its own parentheses [OK]

Common Mistakes:

• Omitting parentheses around grouping sets
• Thinking SUM() is incompatible with GROUPING SETS
• Confusing GROUP BY multiple columns with GROUPING SETS syntax

5. You want to create a report showing total sales grouped by product, by region, and by both product and region together. Which GROUPING SETS clause achieves this in one query?

hard

A. GROUP BY GROUPING SETS ((product), (region), (product, region))

B. GROUP BY product, region

C. GROUP BY GROUPING SETS (product, region)

D. GROUP BY CUBE (product, region)

Solution

1. Step 1: Understand required groupings

   We need three groupings: by product alone, by region alone, and by both together.

2. Step 2: Match with GROUPING SETS syntax

   GROUPING SETS ((product), (region), (product, region)) explicitly lists all three groupings.

3. Step 3: Evaluate other options

   GROUP BY product, region groups by both columns together only; C is invalid syntax; D (CUBE) includes all combinations but is not GROUPING SETS.

4. Final Answer:

   GROUP BY GROUPING SETS ((product), (region), (product, region)) -> Option A

5. Quick Check:

   Explicit sets list all needed groupings [OK]

Hint: List all groupings inside GROUPING SETS parentheses [OK]

Common Mistakes:

• Using GROUP BY without GROUPING SETS for multiple groupings
• Confusing CUBE with GROUPING SETS
• Incorrect syntax without nested parentheses