Practical insights
- 1000published
- 25in review
- 8topic families
Results
- Write down the grain of every table and assert it before the first aggregate
You start a KPI query on an unfamiliar table, or a table whose definition changed recently.
easydocumented fact - Deduplicate on a business key and keep the latest version by update time, not with DISTINCT
A raw table contains repeated rows for the same flight and date, some identical and some with a revised revenue value.
easypractitioner heuristic - Normalize categorical keys and compare their cardinality with a reference list before grouping
A GROUP BY route returns more distinct routes than the network has, including near-identical codes.
easypractitioner heuristic - Distinguish "zero", "unknown" and "not applicable" instead of letting one NULL mean all three
A cancellations column is NULL for some flights, and analysts disagree on whether that means no cancellations, missing data or a flight that never operated.
easypractitioner heuristic - Encode impossible values as explicit integrity rules that quarantine rows and count them
EDA finds load factors above 1 and negative bookings in a raw table that feeds a forecast.
easypractitioner heuristic - Track distinct-value counts per column as an early warning for upstream changes
A model or dashboard depends on categorical columns fed by systems you do not own.
easypractitioner heuristic - Check source freshness against an explicit SLA, more often than the SLA itself
A morning revenue dashboard occasionally shows yesterday's numbers unchanged because an upstream load failed silently.
easydocumented fact - Check row volume per entity and period to find gaps that schema tests cannot see
A table passes all type and null checks, yet a route's history has a hole of several days.
easypractitioner heuristic - Write chart titles that state the finding and its scope, not the variables plotted
A slide is titled "Bookings by month, 2023-2024" and the presenter explains the point verbally.
easypractitioner heuristic - Spell out the window frame when you use LAST_VALUE or NTH_VALUE
A query takes the "latest fare in the booking window" with LASTVALUE(fare) OVER (PARTITION BY flightno ORDER BY snapshotday) and returns the current row's own fare on every row.
easydocumented fact - A negated filter drops NULL rows, so write the NULL branch explicitly
A query keeps "flights not affected by an event" with WHERE event < 'strike', and the analyst expects every other flight to remain.
easydocumented fact - Do money arithmetic in an exact numeric type and compare floats with a tolerance
A reconciliation sums millions of fare amounts stored as double precision, and a total differs from the ledger by a few cents that move when the query plan changes.
easydocumented fact - Page on actionable conditions only, and keep everything else on the dashboard
A data-platform team routes every failed check, slow query and late table to a chat alert, and the channel is muted within a month.
easydocumented fact