Module 3 · From question to insight Lesson 8 of 15
Sanity-checking your own numbers
A wrong number presented confidently is worse than no number. Row counts, totals and a second method for the same figure are how you catch it before your manager does.
Worked example
If your monthly total is 10x the yearly total, the join multiplied the rows — a duplicated key in one table, and a mistake that reaches a report once a week somewhere.
Your practice task
For one of your queries, check the row count before and after the join and verify the total against the raw table.
Do this before moving on. Reading a solution teaches the shape of it; typing it teaches you.
Key takeaway
A wrong number presented confidently is worse than no number. Row counts, totals and a second method for the same figure are how you catch it before your manager does.
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