Blog, page 11

Field notes — one a day since May 2023. Things we shipped, things we broke, and numbers we went and checked.

2026 2025 2024 2023

1,200 posts. , or browse by year and tag below.

Dec 11, 2025

Finding the gaps in data-job-postings

gaps and islands against a real schema, and the clause in it that is doing the work.

sql Analytics engineering

Dec 10, 2025

9.9% of week12_score is missing

89 blanks in one column, and the one-line check that decides whether dropping them is free.

quality statistics Statistics

Dec 9, 2025

The average line no is not the typical one

A 58.5% gap between mean and median on one column, and which of the two answers the question you were asked.

statistics practice Statistics

Dec 8, 2025

Five minutes with account_id in saas-subscriptions

2,500 rows, all distinct, and the one fact about account_id that changes how you query it.

quality practice Data quality

Dec 7, 2025

The arithmetic behind a cheap query

Column pruning times partition pruning on a real schema, and the function call that quietly defeats both.

performance warehousing Data platform

Dec 6, 2025

Before you clip the outliers

A max 1.1× the 99th percentile, and the three different things that could be.

statistics quality Statistics

Dec 5, 2025

bmi by arm: a 0% spread

Real group means for one column across 2 segments, and what the pooled average conceals.

statistics practice Analytics practice

Dec 4, 2025

A weak correlation, and what it is not

A measured correlation of 0.25 between two columns, what its square says, and the diagnostic that costs one line.

statistics Statistics

Dec 3, 2025

Correction: Lookback window

The page claimed more than it should have. What it says now, and where the pattern stops applying.

quality practice Data engineering

Dec 2, 2025

Charting salary_min_usd by city

Two facts about the columns decide the chart. Cardinality and skew, in that order.

visualization Visualization

Dec 1, 2025

Why Data Explorer works the way it does

A fast table with per-column profiling: type inference, missing counts, distinct values, quantiles, and a sparkline distribution for every numeric column.

visualization Visualization

Nov 30, 2025

An exercise on sensor-telemetry

Eight thousand readings from twelve machines across three sites, at ten-minute intervals, with drift, seasonal temperature, injected anomalies, and gaps where a gateway dropped offline..

quality practice Data quality

Nov 29, 2025