var query=from t1 in dt1.AsEnumerable() //菜单表
let temp=dt2.AsEnumerable().Where(t2=>t2.Field<int>("父菜单ID")==1).Select(t2=>t2.Field<int>("子菜单ID"))
where temp.Contains(t1.Field<int>("識別碼"))
select t1;
var query=from t1 in dt1.AsEnumerable() //菜单表
let temp=dt2.AsEnumerable().Where(t2=>t2.Field<int>("父菜单ID")==1).Select(t2=>t2.Field<int>("子菜单ID"))
where temp.Contains(t1)
select t1;