Sentinel Values: The Hidden Cost of 0, -1, "1900-01-01" and 9999-12-31
Sentinel values (0 in salary, 9999-12-31 in an end date, 1900-01-01 in a date) silently corrupt aggregates: in the example the average salary comes out as 51,000 instead of 85,000. The fix is usually a nullable column, a separate state field when absence has several meanings and a Special Case type in the domain; a sentinel can be a deliberate standard only when a single producer owns it (temporal tables, a persisted computed column).
7 Nov 2026
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15 min
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