Validate Domain

The is_valid_domain function validates a domain name against RFC 1035 / RFC 1123 rules. Returns a BOOLEAN.

Validation rules:

• Total length: 1–253 characters

• At least two labels separated by dots (e.g., example.com)

• Each label: 1–63 characters, alphanumeric and hyphens only

• Labels must not start or end with a hyphen

• TLD must not be all-numeric (rejects IP addresses)

• Optional trailing dot (FQDN notation) is allowed

D SELECT is_valid_domain('example.com') AS valid;
┌─────────┐
│  valid  │
│ boolean │
├─────────┤
│ true    │
└─────────┘

D SELECT is_valid_domain('sub.example.co.uk') AS valid;
┌─────────┐
│  valid  │
│ boolean │
├─────────┤
│ true    │
└─────────┘

D SELECT is_valid_domain('localhost') AS valid;
┌─────────┐
│  valid  │
│ boolean │
├─────────┤
│ false   │
└─────────┘

D SELECT is_valid_domain('-bad.com') AS valid;
┌─────────┐
│  valid  │
│ boolean │
├─────────┤
│ false   │
└─────────┘

Returns NULL for NULL input.