I have 2 columns 'id' and 'date' in a table, I want to avoid to insert repeated dates for the same id, I mean

```
id  |  date 
------------------
1  | 01/01/2015 
2  | 01/01/2015
3  | 02/01/2015
1  | 01/01/2015 <--- this value is already insert for id 1, and should not be allowed for id 1

```