# Troubleshooting ### Many-to-Many Join Warning If you are seeing this warning, it means the join between the first dataset can match many items in the second dataset, and vice-versa. ### Why this is risky: * In a many-to-many join, the result includes every combination of matches from both tables (A matches × B matches). * That means the same record is repeated once for each match on the other table, which can overcount totals and distort aggregations e.g. averages, sums, etc. * Unlike a one-to-many join (where only the “one” side repeats), both sides repeat here, so errors grow much faster and queries can get large and slow. Example: AdClicks joined to Orders on user\_id. A user can have many clicks and many orders, so the join returns every click×order pair. If a user has 5 clicks and 2 orders, the join yields 10 rows—so counting orders or summing order\_amount is inflated by 5×. #### What you can do: * If you expected a single match, check your join fields are unique. * If you only need totals, make a dataset that summarizes or deduplicates before joining. * Add filters to limit matches. If you want to move forward with the join anyway, we recommend adding a context node to the tables explaining the purpose of the join and the relationship between the two tables.