Data & SQL21 categories
Is my GROUP BY lying to me?
Any aggregation that feeds a number somebody will act on.
Review the aggregation only. First tell me what one output row represents. Then check: does a non-aggregated column vary within its group, are zero-row groups missing from the output entirely, and is anything averaging a ratio that should be a ratio of sums? Show the corrected fragment wherever it is wrong. Query:
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Correctness checks. Catching the join that duplicates rows, the NULL that drops them, and the GROUP BY that lies.
Related prompts
Check this query before I run itBefore running anything expensive, destructive, or going into a report.Find where this join is duplicating rowsYour totals are suspiciously round multiples of what they should be.Check my aggregation for grouping trapsAny query with GROUP BY that feeds a number someone will act on.Hunt every NULL trap in this queryWhen a count came back lower than expected and nothing looks wrong.Can any of these joins multiply rows?Totals look inflated and you suspect the join before the data.Am I counting the right thing?A count feeds a number someone will act on.
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