Consider the table Employee:

```
Department number      Employee_id      Salary
   1                       123           2000
   1                       234           3266
   1                       657           3265
   2                       546           2050
   2                       657           3000
   2                       121           6000
   3                       131           6500
   3                       141           5000
   3                       151           1050

```

Now I want to retrieve the employee\_id having highest salary from each department. How to write the query for this?