Practice
How do you check that a query or spreadsheet you built gives the right answer?
Read first: a sample answer
Fictional sample answer written by JoRoute to show the shape of a strong answer. Do not copy it: replace every detail with what is true for you.
I check every query against a total I already trust. For example, when I wrote a SQL query for monthly revenue in 2023, I compared its January figure with the finance team's closed books and found a gap of $14,000. The cause was refunds counted twice through a join. I fixed the join, tested edge cases like zero-value orders, and kept a short Excel sheet of the checks. Now every report I build has a reconciliation step before anyone sees it.