SQL pattern · P20 · 14 problems

Pivoting and reshaping

Graded problems on pivoting and reshaping, from easy to hard.

14 problems · about 2 h 40 min in all
Start with problem 01Total revenue per category as columns · 7 min
Learn it first · P20The pivot that duplicates a customerAn extra GROUP BY column changes the grain, so one customer becomes several rows.Read the lesson →

Easy

1 problem · about 7 min
01Total revenue per category as columns7 min →

Medium

10 problems · about 1 h 40 min
02Pivot monthly revenue into category columns8 min →03Order counts by status as columns8 min →04Electronics revenue share per month9 min →05Unpivot category totals back to long form10 min →06Crosstab with row totals and a grand-total row12 min →07Two metrics per category in one pivot13 min →08Per-customer order counts by status11 min →09Distinct order statuses per customer7 min →10Distinct product categories per order8 min →11Roll order line items into one row per order12 min →

Hard

3 problems · about 51 min
12Pivot a messy attribute log into one row per device25 min →13Pivot revenue into category columns per customer14 min →14Pivot: zero vs. NULL for missing buckets12 min →
Up next · P21

The join that finds only immediate children

11 practice problems. A single self-join follows one level; a recursive CTE repeats it to every descendant.

Practise P21Read P21