When to normalize (separate tables):
├── Data is repeated across rows
├── Updates would need multiple changes
├── Relationships are clear
└── Query patterns benefit

When to denormalize (embed/duplicate):
├── Read performance critical
├── Data rarely changes
├── Always fetched together
└── Simpler queries needed

Primary Key Selection

Type	Use When
UUID	Distributed systems, security
ULID	UUID + sortable by time
Auto-increment	Simple apps, single database
Natural key	Rarely (business meaning)

Timestamp Strategy

For every table:
├── created_at → When created
├── updated_at → Last modified
└── deleted_at → Soft delete (if needed)

Use TIMESTAMPTZ (with timezone) not TIMESTAMP

Relationship Types

Type	When	Implementation
One-to-One	Extension data	Separate table with FK
One-to-Many	Parent-children	FK on child table
Many-to-Many	Both sides have many	Junction table

Foreign Key ON DELETE

├── CASCADE → Delete children with parent
├── SET NULL → Children become orphans
├── RESTRICT → Prevent delete if children exist
└── SET DEFAULT → Children get default value

scripts

database-selection.md