Fx MIN GROUP BY unable to spot the expression error

[Luganega]

Good day everybody!

I'm a newbie in Looker. Currently i have created a simple Look with 3 columns.

Columns A: Vessel name / columns B: Port call / column C: date of call (all 3 fields are dimensions)

In my Look every vessel calls more than one port. 

Now I would likes to calculate in column D the Min date of call for each Vessel. 

I have already tried with: Min (date of call) over (partition by Vessel name) but It does not work... Same result with Min (date of call) group by Vessel name

Has anyone suggestion to solve this problem? Thnks