encontre esta forma de consultar a 4 tablas no-dependientes, haciendo uso del UNION ALL
Código PHP:
(SELECT LOGIN, CONTRASENA FROM franquiciador WHERE (LOGIN=%s AND CONTRASENA=%s))
UNION ALL
(SELECT LOGIN, CONTRASENA FROM franquiciado WHERE (LOGIN=%s AND CONTRASENA=%s))
UNION ALL
(SELECT LOGIN, CONTRASENA FROM inversionista WHERE (LOGIN=%s AND CONTRASENA=%s))
UNION ALL
(SELECT LOGIN, CONTRASENA FROM proveedor WHERE (LOGIN=%s AND CONTRASENA=%s))
Código PHP:
$LoginRS__query=sprintf("SELECT LOGIN, CONTRASENA FROM franquiciado WHERE LOGIN=%s AND CONTRASENA=%s",
GetSQLValueString($loginUsername, "text"), GetSQLValueString($password, "text"));
Saludos