Here is my problem:  

I have a table with categories and I want to rank them:

```
category
dog
cat
fish
dog
dog

```

What I want is to add a column and to rank them:

```
category       rank    
dog             1  
cat             2
fish            3
dog             1
dog             1

```

* Sorry for the terrible table (help in writing normal tables in stack overflow would be great, too)
* Any ideas about how to add the rank column?

Thanks!