Find Bad Numbers and Dates in PostgreSQL 16+
Find invalid numbers and dates in PostgreSQL 16+, preserve raw values, audit rejected rows, and reconcile imports with tested SQL examples.
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SQL Tutorials and Guides
Explore SQL tutorials, practical examples, and interview preparation guides from SQLPad.
SQL Server NOLOCK: Get Consistent Report Totals
Learn why SQL Server NOLOCK changes report totals, reproduce a dirty read, and choose RCSI or SNAPSHOT for consistent concurrent reporting.
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SQL vs Python: Choosing an Analysis Workflow
Choose where SQL and Python should run, define reliable data handoffs, compare costs, and avoid duplicating business logic across tools.
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How to Test SQL Queries With Expected Results
Test SQL queries with expected rows, duplicate-aware comparisons, boundary cases, and deliberate failures before trusting report results.
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Turn a One-Off SQL Query Into a Reliable Weekly Report
Build reliable recurring SQL reports with fixed periods, validation gates, safe reruns, late-data revisions, and a practical handoff runbook.
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How to Explore an Unfamiliar Database Without Documentation
A safe, read-only workflow for exploring an unfamiliar database, finding relationships, profiling data, and validating results without documentation.
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How to Build a SQL Query From Scratch
Turn a business prompt into working PostgreSQL with a framework for grain, joins, CTEs, validation, edge cases, and interview explanations.
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How to Learn From SQL Mistakes With an Error Log
Turn wrong SQL answers into lasting skill with a practical error log, hint ladder, counterexample, and spaced-review routine for interviews.
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SQL Dialects in Interviews: PostgreSQL vs MySQL vs SQL Server
Translate interview SQL across PostgreSQL, MySQL, and SQL Server for dates, row limits, intervals, strings, nulls, casting, and window functions.
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Where to Practice SQL Interview Questions for Data Analyst Roles
Choose SQL interview practice resources with a clear plan: syntax drills, messy data, live rounds, business cases, and a weekly schedule for analysts.
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SQL Interview Speed Drills: Solve 3 to 5 Questions in 30 Minutes
Practice timed SQL interview rounds with a repeatable plan for reading prompts, choosing patterns, testing joins, and solving 3 to 5 questions in 30 minutes.
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How to Fill Missing Values in SQL Without Hiding Data Quality Problems
Fill missing values in SQL with COALESCE, window functions, lookup tables, and audits while preserving data quality and avoiding silent mistakes.
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SQL Server for Data Analysts: T-SQL Patterns, Traps, and Interview Prep
Learn the T-SQL patterns analysts need for SQL Server interviews and jobs: TOP, APPLY, temp tables, dates, windows, nulls, and plans.
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From Excel to SQL: A Practical Workflow for Analysts Who Inherit Spreadsheet Chaos
Move spreadsheet-heavy analyst work into SQL safely with staging tables, validation checks, refresh cadence, and Power Query handoff patterns.
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LeetCode SQL 50 vs Real Data Analyst Interviews: What to Practice
Use LeetCode SQL 50 wisely, then practice the messy analyst patterns interviews actually test: grain, joins, nulls, metrics, and time pressure.
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Live SQL Interview Prep: How to Handle 45-Minute Query Rounds
Prepare for live SQL interviews with a timed structure, talk-through strategy, pattern checklist, and recovery plan for analyst roles.
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Retail SQL Interview Case Study: Product and Category Performance
Practice a realistic retail SQL interview case with category sales, AOV, top products, margin, inventory risk, and business interpretation.
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Debug Long SQL Queries in Interviews
A practical workflow for reading long SQL interview queries: trace CTEs, inspect joins, validate grain, and make safe changes under pressure.
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GROUP BY vs PARTITION BY: A Window Function Mental Model
Understand GROUP BY vs PARTITION BY with a practical window-function mental model, examples, ranking patterns, and interview mistakes to avoid.
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SQL Data Modeling for Analyst Interviews: Grain, Keys, Normalization, and ER Diagrams
Learn the data modeling concepts analyst interviews expect: grain, keys, cardinality, normalization, ER diagrams, views, and validation queries.
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SQL Logical Query Processing Order: FROM, WHERE, GROUP BY, HAVING, SELECT
Learn SQL logical query processing order, why aliases fail in WHERE, where LEFT JOIN filters belong, and how to explain execution order in interviews.
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Does SQL LIMIT Read All Rows? ORDER BY, Indexes, and Keyset Pagination
Learn when SQL LIMIT can stop early, why ORDER BY may still scan and sort rows, and how indexes and keyset pagination fix top-N queries.
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PostgreSQL JSONB Insert Performance: Why Bulk Loads Slow Down and What to Do
PostgreSQL JSONB insert performance guide with benchmark workflow, COPY limits, GIN index costs, staging patterns, and production checklist.
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ROW_NUMBER vs RANK vs DENSE_RANK: Top-N SQL Interview Patterns and Tie Rules
ROW_NUMBER vs RANK vs DENSE_RANK guide for top-N per group, ties, deterministic ordering, NULL handling, QUALIFY, and SQL interviews.
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SQL CASE WHEN for Interviews: Conditional Aggregation, NULLs, and the COUNT Trap
SQL CASE WHEN interview guide with conditional aggregation, COUNT traps, NULL handling, FILTER syntax, result tables, and checklist.
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How to Remove Duplicates in SQL: DISTINCT vs ROW_NUMBER
Learn how to remove duplicates in SQL with DISTINCT, GROUP BY, ROW_NUMBER, QUALIFY, and safer delete patterns that keep the right row.
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Dynamic SQL Pivot: How to Pivot on Unknown Columns Safely
Learn how to build a dynamic SQL pivot for unknown column values, when to use it, and when conditional aggregation or a BI tool is safer.
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SQL GROUP BY Errors: WHERE vs HAVING and the Bare Column Mistake
Fix common SQL GROUP BY errors, including WHERE vs HAVING confusion, bare columns, and MySQL ONLY_FULL_GROUP_BY failures.
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SQL Median and Percentiles: PERCENTILE_CONT, PERCENTILE_DISC, and the Grouping Mistakes That Change Your Answer
Learn how SQL median and percentile functions work, when to use PERCENTILE_CONT or PERCENTILE_DISC, and how grouping mistakes change the answer.
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How to Read SQL EXPLAIN Plans Without Guessing: Costs, Rows, EXPLAIN ANALYZE, and the Bottleneck That Actually Matters
Learn how to read SQL EXPLAIN and EXPLAIN ANALYZE plans, interpret costs and row estimates, and diagnose the bottleneck that actually makes a query slow.
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SQL Date Spines and Calendar Tables: Build Complete Time Series Without Missing Days
Learn when to use a date spine or calendar table in SQL for cohorts, business-day logic, and gap-free time series in Postgres and MySQL.
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SQL CTE vs Subquery vs Temp Table: How to Choose the Right Pattern
Learn when a CTE, subquery, or temp table is the right SQL tool, including performance tradeoffs, readability, reuse, and interview-ready explanations.
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Recursive CTEs in SQL: Hierarchies, Paths, Cycle Checks, and Debugging
Learn how recursive CTEs work in SQL, how to debug runaway recursion, and how to model hierarchies, paths, and date expansion safely.
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SQL COUNT with LEFT JOIN: Zero Rows, DISTINCT, and Many-to-Many Traps
Learn how COUNT behaves after LEFT JOINs, why COUNT(*) and COUNT(column) give different answers, and how to avoid inflated totals in many-to-many joins.
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Why SQL Indexes Are Not Used: Sargability, Column Order, and Full-Scan Traps
Learn why SQL indexes get ignored, how sargable predicates work, and which query patterns force scans even when an index exists.
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SQL Funnel Queries for Event Data: Daily Conversion Rates Without Inflated Counts
Build SQL funnel queries from event data without inflated counts by defining the cohort, reducing each step to one row per user, and enforcing step order.
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SQL Latest Row Per Group: ROW_NUMBER, QUALIFY, and Tie-Breakers That Keep Results Deterministic
Learn deterministic latest-row and top-N-per-group SQL patterns across PostgreSQL, BigQuery, Snowflake, MySQL, and SQL Server.
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SQL Window Frames Explained: ROWS vs RANGE, Running Totals, and the Default That Changes Your Results
Understand SQL window frames with ROWS vs RANGE, CURRENT ROW semantics, LAST_VALUE, and the default frame behavior that changes results.
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SQL Retention Queries: Cohorts, Return Windows, and the Edge Cases That Break Them
Learn how to write SQL retention queries correctly by defining cohorts, return windows, user-level counting, and incomplete-period edge cases first.
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How to Solve Gaps and Islands SQL Interview Questions with LAG and ROW_NUMBER
Use repeatable SQL patterns for gaps and islands interview questions, including streaks, sessions, state changes, and grouped runs with LAG and ROW_NUMBER.
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SQL NULL Logic for Interviews: NOT IN, NOT EXISTS, and LEFT JOIN Filters Without Silent Bugs
Learn the SQL NULL traps that break interview answers: three-valued logic, COUNT(column), NOT IN vs NOT EXISTS, and LEFT JOIN filters.
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SQL Date and Timestamp Interview Questions: Parsing, Bucketing, and Filtering Without Off-by-One Mistakes
Master SQL date and timestamp interview questions with practical patterns for parsing, bucketing, and filtering time ranges in Postgres and MySQL.
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How to Answer Vague SQL Interview Questions by Defining Grain, Metrics, and Assumptions
Learn how to handle vague SQL interview prompts by defining grain, metrics, assumptions, and validation before you start typing.
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PostgreSQL JSONB vs Columns: When Flexibility Becomes a Performance Problem
Learn when PostgreSQL JSONB is a good fit, when regular columns are better, and how indexing and query patterns affect performance.
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Why SQL Joins Create Duplicate Rows and How to Fix Them Without Hiding the Problem
Learn why SQL joins create duplicate rows, how grain mismatch causes row explosion, and how to fix the real problem without overusing DISTINCT.
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MySQL DATETIME vs TIMESTAMP: Time Zone Rules That Cause Production Bugs
Learn the real difference between MySQL DATETIME and TIMESTAMP, how timezone conversion works, and why the wrong choice causes application bugs.
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Natural Log Calculations in SQL (Postgres and MySQL)
A long-form SQL guide to natural log calculations in Postgres/MySQL with safe CASE logic, grouped metrics, window growth patterns, and production tips.
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Best SQL Books - 2024
Discover the best books for SQL in 2024. Enhance your database management skills with top picks for beginners to experts. Learn SQL now!
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SQL Query: Retrieve First Day of Month Across Multiple Platforms
Learn how to fetch the first day of a month in SQL using various platforms like PostgreSQL, MySQL, SQL Server, Oracle, Snowflake, and Spark with code example…
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Mastering SQL Pivot: Convert Rows to Columns Efficiently
Learn how to efficiently convert rows to columns using pivot in SQL. This comprehensive guide covers examples for multiple platforms.
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