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20,926 resources · Page 79 of 872
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SQL Cheat Sheet for Interviews: Clauses, Joins, Windows, and NULL Traps
A scannable PostgreSQL cheat sheet for NULLs, date ranges, joins, counts, denominators, windows, ties, and logical query order.
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SQL Churn Interview Questions: Reactivation, Pauses, and Subscription Boundaries
Practice SQL churn interview questions with tested queries for account loss, reactivation, paused billing, overlapping subscriptions, and cutoff boundaries.
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SQL COALESCE: Syntax, Engine Differences, and the NULL Traps Interviewers Test
SQL COALESCE, explained: syntax, COALESCE vs ISNULL/IFNULL/NVL, the aggregate and index traps, plus real interview questions from Meta and TikTok.
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SQL Conversion Rate Interview Questions: Eligibility, Grain, and Denominator Traps
Solve SQL conversion rate interview questions with tested eligibility rules, user and session grains, duplicate orders, mature cohorts, and denominator checks.
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SQL COUNT: COUNT(*) vs COUNT(column) vs COUNT(DISTINCT), and the Traps Interviewers Test
Understand SQL COUNT through verified examples of rows, NULLs, distinct entities, outer joins, conditional counts, and join fanout.
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SQL CTE (WITH Clause): Chaining, CTE vs Subquery, and Recursive CTEs
Learn PostgreSQL CTE scope, grain-first chaining, derived-table equivalence, cycle-safe recursion, and dense date spines with verified outputs.
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SQL Customer Lifetime Value Interview Questions: Cohorts, Refunds, and Observation Windows
Practice SQL customer lifetime value interview questions with cohort denominators, partial refunds, 90-day windows, tested queries, and clear LTV limits.
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SQL Data Sampling Interview Questions: Random Rows, Stratification, and Reproducibility
SQL data sampling interview questions: compare random rows and blocks, define strata and weights, and reproduce samples with stable keys and snapshots.
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SQL Data Validation Interview Questions: Reconcile a Migration Before Sign-Off
Reconcile a data migration with SQL key checks, NULL-aware row diffs, aligned snapshots, business invariants, and explicit sign-off evidence.
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SQL Date Functions: DATE_TRUNC, EXTRACT, Interval Math, and Time Zone Traps
Use PostgreSQL date functions safely across time zones, month buckets, ISO calendars, intervals, half-open windows, and dense rolling periods.
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SQL Date Spine Interview Questions: Fill Missing Dates Without Inflating Metrics
Build SQL date spines without inflating metrics: define eligible keys, aggregate facts first, preserve empty days, and validate totals.
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SQL Deduplication Interview Exercise: Keep the Latest Valid Record, Not Just the Latest Timestamp
Practice SQL deduplication with validity rules, authoritative versions, deletion markers, conflict quarantine, and replay-safe expected results.
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SQL SELECT DISTINCT: What It Actually Deduplicates, and When It Hides a Bug
Understand SQL DISTINCT across full rows, NULLs, counts, groups, latest-row selection, and join fanout using verified PostgreSQL outputs.
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SQL for Data Analysis: The Six Query Patterns Analyst Interviews Actually Test
Learn six practical PostgreSQL patterns for analyst work: conditional metrics, retention, deduplication, rolling averages, sessions, and data quality.
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SQL Fraud Detection Interview Questions: Velocity Windows, Shared Devices, and False Positives
Practice SQL fraud detection interview questions with velocity windows, shared devices, point-in-time features, false positives, and tested query examples.
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SQL Gaps and Islands: Finding Consecutive Runs, Streaks, and Sessions
Solve SQL gaps and islands with deduplicated date streaks, active-month runs, threshold sessions, state changes, and explicit missing ranges.
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SQL GROUP BY, Aggregate Functions, and HAVING Explained
Learn GROUP BY grain, NULL-aware aggregates, WHERE versus HAVING, duplicate keys, conditional metrics, and distinct membership in PostgreSQL.
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SQL GROUPING SETS Interview Questions: Subtotals, NULLs, and Double Counting
Practice SQL GROUPING SETS with a worked subtotal query, GROUPING masks, real versus generated NULLs, duplicate rows, and reconciliation checks.
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SQL IN Operator: Subqueries, NOT IN, and the NULL Trap That Returns Zero Rows
How SQL IN works, why one NULL can make NOT IN return zero rows, and when data science candidates should use NOT EXISTS or an anti-join.
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SQL Injection Interview Questions: Bind Parameters, Dynamic Identifiers, and ORM Boundaries
Practice defensive SQL injection interviews with a value-versus-identifier repair matrix, ORM boundaries, and safe regression cases.
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SQL Inventory Interview Questions: Stock Movements, Stockouts, and Negative Balances
Solve SQL inventory interview questions with tested stock movements, opening balances, stockout durations, tied timestamps, and negative-stock checks.
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SQL Joins: Every Join Type with Runnable Examples and Exact Results
Learn SQL joins through verified INNER, LEFT, RIGHT, FULL, CROSS, composite-key, self, anti, and fanout-safe PostgreSQL examples.
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SQL LATERAL and APPLY Interview Questions: Top-N per Row and Missing Matches
Practice SQL LATERAL and APPLY interview questions with per-row Top-N, eligibility filters, stable ties, missing matches, and window alternatives.
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SQL Not Equal: <> vs !=, and the NULL Traps That Follow
SQL not equal explained: <> vs !=, why inequality filters silently drop NULL rows, NOT IN vs NOT EXISTS, IS DISTINCT FROM, and case-sensitivity traps.