Database Constraint Design Patterns

Design database constraints for:

Schema:
```sql
[PASTE YOUR SCHEMA]
```

Business Rules:
[LIST BUSINESS RULES TO ENFORCE]

Requirements:
- Constraint types needed: [CHECK/UNIQUE/FK/EXCLUSION]
- Error handling: [HOW TO HANDLE VIOLATIONS]
- Performance considerations: [YES/NO]

Please provide:
1. Constraint definitions with DDL
2. Check constraints for business rules
3. Unique constraints including partial
4. Foreign key with cascade options
5. Exclusion constraints (PostgreSQL)
6. Constraint naming conventions