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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 pathDebugging scenarioCoding problem

Recommended start

Execution Plan Diagnosis

Uses an actual execution plan, row-flow evidence, runtime measurements, and representative parameters to diagnose a slow query without guessing.

Hard~12 minStep 1 of 4

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1Execution Plan DiagnosisRecommended startUses an actual execution plan, row-flow evidence, runtime measurements, and representative parameters to diagnose a slow query without guessing.Debugging scenarioHard~12 minSQLSQL ServerPractice 2

Practice order

4 drillsOne at a time

1Execution Plan DiagnosisUp next / Hard / ~12 min
2Local Date, UTC RangeHard / ~35 min
3Atomic Inventory ReserveMedium / ~25 min

Local Date, UTC Range

Converts local-day boundaries to UTC once, preserving correct daylight-saving behavior and index use on stored UTC timestamps.

Coding problemHard~35 minSQLSQL Server

Practice

3Atomic Inventory ReserveUses a conditional update and transaction to prevent overselling while recording the reservation consistently.Coding problemMedium~25 minSQLSQL ServerPractice

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

4

Deduplicate Imports

Medium / ~25 min

Correctness & Performance - SQL Practical Query Problems | Aporeon