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Pattern

Set logic

13 problemsin this pattern, climbing easy → medium → hard. Pick wherever you're calibrated.

EZ

Easy

0 / 4 solved

Combine web and mobile events
SQL · ~4 min
NEW
Users active on BOTH web and mobile
SQL · ~5 min
NEW
Customers in both BI and finance
SQL · ~5 min
NEW
All distinct customers across both systems
SQL · ~5 min
NEW

MD

Medium

0 / 5 solved

Customers active in BOTH halves of May
SQL · ~8 min
NEW
Total transactions across two payment processors
SQL · ~6 min
NEW
Eligible customers (signups − unsubscribed − bounced)
SQL · ~7 min
NEW
Customers in BI but not finance
SQL · ~6 min
NEW
Customers in exactly one system
SQL · ~8 min
NEW

HD

Hard

0 / 4 solved

Multiset difference — EXCEPT ALL
SQL · ~10 min
NEW
BI vs Finance — customer-list reconciliation
SQL · ~12 min
NEW
Eligible customers after every exclusion list
SQL · ~10 min
NEW
Which system(s) each customer belongs to
SQL · ~11 min
NEW