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Pre-aggregates two one-to-many relationships before joining them to prevent fanout from corrupting financial totals.
Builds several daily business metrics in one grouped query while keeping each metric definition explicit.
Uses an ordered window aggregate to calculate a deterministic running balance per account.
Combines daily aggregation, a calendar table, and a window frame to calculate true seven-calendar-day revenue.
Implements correct half-open interval overlap logic for booking validation.
Explains join behavior using API-shaped data, missing related rows, and result-cardinality trade-offs.
Compares offset and keyset pagination for stable API lists, large tables, and user-facing result consistency.
Explains SQL three-valued logic, null-safe filters, optional relationships, and API behavior around missing values.
Uses EXISTS instead of a row-multiplying join when the related table is only a filter.
Groups normalized email values to identify duplicates before adding or repairing a uniqueness rule.
Uses the gaps-and-islands pattern to find consecutive login-day streaks after deduplicating same-day activity.
Solves a many-to-many all-match filter with grouping and a deliberate empty-selection rule.
Uses NOT EXISTS to express an anti-join without null traps or duplicate parent rows.
Uses a recursive CTE to return hierarchy depth and a readable root-to-node path.
Implements descending keyset pagination with a compound cursor and stable ordering.
Ranks duplicate import rows, previews the deletion set, and removes older copies with deterministic retention.
Writes a left-join aggregate that keeps active customers with no paid orders and applies date filters without changing join semantics.
Uses ROW_NUMBER with a deterministic tie-breaker to return the complete latest status row per order.
Aggregates product sales and ranks independently inside each category with a deterministic top-N rule.
Shapes an API list from its contract and cardinality, projecting only required values while preserving authorization, stable pagination, bounded nesting, index support, and measurable query cost.
Explains aggregate queries, grouping keys, filters before and after aggregation, and business-count correctness.
Uses ROW_NUMBER with deterministic partition ordering to return one complete latest row per group, then evaluates index support, tie semantics, scale, and read-model alternatives.