GROUPING SETS for multiple groupings in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of GROUPING SETS in SQL?

GROUPING SETS lets you group data by multiple combinations of columns in one query. It helps you get several groupings without writing many queries.

beginner

How does GROUPING SETS differ from using multiple GROUP BY queries?

GROUPING SETS combines multiple grouping queries into one. This saves time and makes the query easier to read and faster to run.

intermediate

Write a simple example of GROUPING SETS to group sales by region and product separately.

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

intermediate

What does the GROUPING() function do when used with GROUPING SETS?

GROUPING() tells you if a column is aggregated or not in the current row. It returns 1 if the column is not grouped (aggregated), 0 if it is grouped.

advanced

Can GROUPING SETS be combined with other grouping methods like ROLLUP or CUBE?

Yes, GROUPING SETS can be combined with ROLLUP and CUBE to create complex grouping combinations in one query.

What does GROUPING SETS ((a), (b)) do in a query?

A Joins tables a and b

B Groups data by both columns a and b together

C Filters rows where a equals b

D Groups data by column a and by column b separately

GROUPING SETS ((a), (b)) creates two separate groups: one by column a and one by column b.

Which SQL clause is used to specify multiple grouping sets?

A GROUP BY GROUPING SETS

B ORDER BY GROUPING SETS

C WHERE GROUPING SETS

D HAVING GROUPING SETS

The GROUP BY GROUPING SETS clause defines multiple grouping sets in one query.

What value does GROUPING(column) return if the column is included in the grouping?

A 1

B 0

C NULL

D -1

GROUPING(column) returns 0 if the column is grouped (not aggregated).

Which of these is NOT a valid grouping method in SQL?

A GROUPING SETS

B ROLLUP

C FILTER

D CUBE

FILTER is not a grouping method; GROUPING SETS, ROLLUP, and CUBE are valid grouping methods.

Why use GROUPING SETS instead of multiple separate queries?

A To combine multiple groupings in one query for efficiency

B To sort data faster

C To filter rows by multiple conditions

D To join tables automatically

GROUPING SETS combines multiple grouping queries into one, making it more efficient.

Explain how GROUPING SETS helps when you want to group data by different column combinations in one query.

Think about grouping sales by region and product separately in one query.

Describe the role of the GROUPING() function when used with GROUPING SETS.

It helps tell if a NULL means no data or aggregated data.