01 / Validate the source
Audit a CSV with DuckDB Before You Trust the Dashboard
Find duplicate IDs, invalid dates, broken amounts, and missing customers before you build a chart.
The SQL field guide
Better answers start with better checks.
Three practical SQL lessons for the moment before you trust a number. Run the example, inspect the failure, and keep the check.
Free examples · Fictional data · No signup
01 / Validate the source02 / Check the grain03 / Define the denominator
02 / Check the grain
Why Your SQL Join Doubled Revenue, and How to Fix It
Reproduce a join that inflates revenue, then reconcile the result at one row per order.
03 / Define the denominator
Calculate Monthly Cohort Retention Without Counting Unfinished Months
Count retained users once and separate a completed month with no activity from a month that has not finished.
A small, reproducible place to start.
Each lesson runs in a fresh local DuckDB session. The CSV lesson needs its sample file in the same folder; the other scripts include their data. The walkthroughs explain the expected results and where the examples stop.
duckdb < csv-audit.sql
duckdb < join-fanout.sql
duckdb < cohort-retention.sqlMake the analysis useful to the next person.
Explore how SyneHQ keeps questions, queries, results, and review together when a useful check becomes a shared workflow.