Dashboard Statistics Fix

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A compact PostgreSQL guide for correcting dashboard counts and latest-weight averages distorted by join fan-out.

Dashboard Statistics Fix is a single-page technical explanation of a PostgreSQL reporting bug involving animals, treatments, and weight records. It shows why joining multiple one-to-many relationships multiplies rows, why counting distinct animals alone does not repair the average, and how to calculate every metric at its own grain. Readers can inspect verified sample values, study a complete query using DISTINCT ON and independent subqueries, and compare the faulty and corrected dashboard outputs.

Highlights

Clear root cause

Explains join fan-out

Complete SQL fix

Uses metric-level grain

Verified metrics

Shows sample outputs

Before and after

Compares wrong and fixed

How to Use

Review the root cause
Start with the Root Cause section to see how joining animals, treatments, and weights multiplies rows and causes both counts and averages to diverge from the underlying records.
Check the expected metrics
Use the Correct Metrics cards and sample-record note to understand the target values for total animals, treated animals, and average latest weight before adapting the query.
Apply the grain-isolated query
Read the SQL block and calculate each dashboard metric from its appropriate source. The latest_weights CTE retains one recent weight per animal, while independent subqueries prevent unrelated treatment rows from changing the average.
Validate the result
Compare your dashboard output with the Before / After table and verify each metric independently against source records before deploying the corrected query.