PL/SQL function defined in SQL WITH clause

plsql_function_in_sql.sql

 
WITH
    FUNCTION get_domain(url VARCHAR2) RETURN VARCHAR2 IS
        pos BINARY_INTEGER;
        len BINARY_INTEGER;
    BEGIN
        pos := INSTR( url, 'www.' );
        len := INSTR( SUBSTR( url, pos + 4 ), '.' ) - 1;
        RETURN SUBSTR( url, pos + 4, len );
    END;
SELECT DISTINCT url, get_domain(url) AS domain
  FROM websites;

             URL    DOMAIN
----------------  --------
  www.oracle.com    oracle
 www.graalvm.org   graalvm