What are common anti-patterns in database design?

Key database anti-patterns: EAV (Entity-Attribute-Value) — storing attributes as rows in a key-value table instead of columns — flexible but destroys query performance and type safety; God table — one massive table with hundreds of columns for everything; Jaywalking — storing multiple values in a single delimited column instead of a proper relation; Implicit columns — using SELECT * in application queries; Soft deletes without care — a deleted_at column that you forget to filter, causing stale data to appear; Missing foreign keys — relying on application code for referential integrity; Over-indexing — adding indexes on every column, slowing writes; Using NULLs for missing meaning — distinguishing "unknown" from "not applicable" with a single NULL.