Correction and Reversal Patterns

The interviewer asks: 'The source system sent incorrect data yesterday and just sent a correction. How does your model handle it?' They are testing whether you destructively update fact rows (no-hire signal) or use reversal patterns that preserve the audit trail (strong-hire signal). In financial data modeling interviews, this question is worth 20% of the scorecard. Why 'Just UPDATE It' Is a No-Hire Answer The Reversal Pattern: The Strong-Hire Answer Your reversal answer: 'Two new rows: a reversal that negates the original (-$1,000) and a correction with the right value ($1,100). The original row is untouched. SUM produces $1,100: correct. The audit trail shows exactly what happened and when.' Walk through the three rows on the whiteboard. The interviewer is checking whether you preserve t