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Correctness & Performance - SQL Practical Query Problems | Aporeon

SQL Practical Query Problems

Correctness & Performance

SARGable time-zone queries, atomic inventory updates, safe deterministic data cleanup, and evidence-led execution-plan diagnosis.

4 drillsPractice one at a timeOrdered pathCoding problemDebugging scenario

Recommended start

Atomic Inventory Reserve

Uses a conditional update and transaction to prevent overselling while recording the reservation consistently.

Medium~25 minStep 1 of 4

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1Atomic Inventory ReserveRecommended startUses a conditional update and transaction to prevent overselling while recording the reservation consistently.Coding problemMedium~25 minSQLSQL ServerPractice 2

Practice order

4 drillsOne at a time

1Atomic Inventory ReserveUp next / Medium / ~25 min
2Execution Plan DiagnosisHard / ~12 min
3Local Date, UTC RangeHard / ~35 min

Execution Plan DiagnosisUses an actual execution plan, row-flow evidence, runtime measurements, and representative parameters to diagnose a slow query without guessing.Debugging scenarioHard~12 minSQLSQL Server

Practice

3Local Date, UTC RangeConverts local-day boundaries to UTC once, preserving correct daylight-saving behavior and index use on stored UTC timestamps.Coding problemHard~35 minSQLSQL ServerPractice

4Deduplicate ImportsRanks duplicate import rows, previews the deletion set, and removes older copies with deterministic retention.Coding problemMedium~25 minSQLSQL ServerPractice

4Deduplicate Imports

Medium / ~25 min