SQL pattern · 11 problems

Data quality & validation

Graded problems on data quality & validation, from easy to hard.

11 problems · about 2 h 10 min in all

Start with problem 01Count duplicate rows per customer_id · 4 min

Easy

4 problems · about 26 min

01Count duplicate rows per customer_id4 min →02How much duplication is in the feed?4 min →03Profile how complete each column is8 min →04Check every foreign key for orphans10 min →

Medium

4 problems · about 45 min

05Find fully-identical duplicate rows6 min →06Find duplicate contacts once the key is normalised12 min →07Which tables have missed their freshness SLA?12 min →08Flag days whose row count jumps or drops15 min →

Hard

3 problems · about 56 min

09Find payment reconciliation breaks18 min →10Reconcile source and warehouse partition by partition20 min →11Report every contract rule a raw row breaks18 min →