[Exim] LDAP to RDBMS

My Exim control local domain and user usign LDAP :

local_domains = ldap;ldap::///ou=Domain, o=NODALIS?domain?sub?(domain=$key)

local_not_exists:
    condition = ${lookup ldap ldap:///o=NODALIS?mailhost?sub?(&(mail=$local_part@
$domain)(servizio=MAIL))} {0}{1}}

I would change with a query SQL using a RDBMS on one other server.

How can i do this?

Thank you