Validate the Merge Before the KPI
Validate merge cardinality, row retention, and unmatched keys before using a joined dataframe for KPI reporting.
stat-tile-trio before-after step-ladder common-trap-callout Leila needs segment revenue, but the invoice table is many rows per customer while the customer segment table should be one row per customer. Validate the intended merge cardinality before calculating the KPI, then audit unmatched rows and metric totals after the join. The common shortcut is to merge first and inspect the dashboard number later. That lets duplicate dimension rows multiply revenue or unmatched keys disappear inside a polished chart. Before A plain merge returns more rows than invoices and revenue rises 11%, but no error is raised. After validate='many_to_one' catches duplicate customer keys before…
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