Complex joins use multiple conditions, non-equality operators, or computed values in ON clause. Goes beyond simple foreign_key = primary_key.

ON clause can have multiple conditions with AND/OR. Can use >, <, BETWEEN for ranges. Can include CASE expressions. Performance depends on indexes and condition selectivity.

Real-world joins often have complex conditions beyond simple equality. Understanding range joins, multiple conditions, and optimization is essential for production queries.

Price history tables join on date ranges. Inventory joins on quantity thresholds. Promotions join on date and customer segments. Audit logs join on time windows.