The missing-value rule nobody wrote down for this column

A column is missing a chunk of its values and three people on the team each fill the gaps a different way.

Beginner to intermediateRead 6 minDoing: under an hour6 steps

▶ Start

What you'll have at the end

One written rule per column, drop the row, fill with a stated value, or flag it unknown, applied consistently.

Before you start

You need

You have a table where one column has real gaps, blank cells or NULLs, not typos, and a way to run a query or count against it, a spreadsheet or a SQL client both work.

Not covered

Statistically guessing the missing value from other columns you already have, useful only when one of those columns actually points to the real answer; this recipe covers the more common case where none of them do.

Leans on

6 steps

Where to go next

Write a reproducible data cleaning log

you need one continuous log covering every cleaning decision across a whole dataset; this recipe writes the rule for a single column.

Checked 26 Aug 2026

Part of the Data Cleaning and Validation for Analysts cookbook