postgresql 函数 sys_guid()

CREATE or REPLACE FUNCTION "sys_guid"() 
RETURNS "pg_catalog"."varchar" AS 
$BODY$ 
DECLARE 
v_seed_value varchar(32); 
BEGIN 
select 
md5( 
inet_client_addr()::varchar || 
timeofday() || 
inet_server_addr()::varchar || 
to_hex(inet_client_port()) 
) 
into v_seed_value; 


return (substr(v_seed_value,1,8) || 
substr(v_seed_value,9,4) || 
substr(v_seed_value,13,4) || 
substr(v_seed_value,17,4) || 
substr(v_seed_value,21,12)); 
END; 
$BODY$ 
LANGUAGE ‘plpgsql‘ VOLATILE SECURITY DEFINER;