Databases · Middle · Question 68 of 75

What does `GROUP BY ROLLUP (country, city)` add to the result?

1Rows sorted by country and city
2Only the grand total
✓Correct answer: Subtotal rows per country and a grand total, in addition to the per-city groups

Explanation

In subtotal rows the rolled-up columns are NULL; GROUPING() tells them apart from real NULLs. CUBE and GROUPING SETS give other combinations.

Further reading

PostgreSQL: Table expressions (FROM, JOIN, WHERE, GROUP BY) ↗

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