Add domain_depth function

[hatamiarash7]

Implements domain_depth(VARCHAR) → INTEGER — returns the number of dot-separated levels (labels) in a domain name. Extracts the host from full URLs automatically.

Examples

SELECT domain_depth('example.com');              -- 2
SELECT domain_depth('https://www.example.com');  -- 3
SELECT domain_depth('a.b.c.example.co.uk');      -- 6
SELECT domain_depth('localhost');                 -- 1
SELECT domain_depth('192.168.1.1');              -- 0 (IP address)

Behavior

• Extracts the host from full URLs (with scheme, port, path, query, fragment) before counting
• Returns the number of dot-separated labels: www.example.com → 3
• Returns 0 for IPv4 and IPv6 addresses (not domains)
• Returns 0 for empty strings and invalid input
• Returns 1 for single-label names like localhost
• Returns NULL for NULL input
• Strips trailing DNS dots before counting (example.com. → 2)
• Case-insensitive