Join Duplication Debugging Workflow

Reading the sketch

1. Confirm the symptom

   Compare row counts and metrics before and after the join.

2. Check aggregation and keys

   Review the aggregation logic and test whether the join keys are unique.

3. Compare table grain

   Check whether both sides of the join describe data at the same grain.

4. Inspect join behavior

   Review the join type and look for unexpected nulls or dropped rows.

5. Trace the cause

   Use the evidence from each check to identify the root cause before changing the query.