Catch a join fan-out that doubles your totals

The dashboard number looks reasonable until someone points out it's exactly double what finance has.

Intermediate to advancedRead 6 minDoing: 15 to 20 minutes once you know the pattern6 steps

What you'll have at the end

The table that's fanning out is found with a before-and-after row count, the query is rewritten to sum the total from a table where each order appears once, and a saved guard query catches the same join if it starts doubling totals again.

Before you start

You need

A SQL query, already running, that joins two tables and sums or averages a column that belongs to one side of that join.

Not covered

Reconciling two reports built on genuinely different metric definitions; this recipe covers a single query that duplicated its own rows.

Leans on

6 steps

Where to go next

Two reports that should reconcile, and currently do not

when the numbers still disagree after this fix, because the two reports were built on different definitions rather than a duplicated join.

Checked 26 Aug 2026

Part of the Data Cleaning and Validation for Analysts cookbook