Issues with Pin Map

DB: MySQL backend
Ver: Metabase v0.17.1

I’m having issues adding a pin map with latitude and longitude values stored in two different columns. They are stored as varchar (I don’t know why the developers decided this), but I’m assuming MB requires them to be in a decimal form? Trying the query below to convert but saying I still need the Latitude and Longitude columns:

select ud.user_id , cast( as decimal(10,8)) as Latitude , cast(ud.lng as decimal(10,8)) as Longitude from user_details ud where date(ud.created_at) >= '2016-06-30'

Any idea what I’m doing wrong here? Or do I misunderstand the instructions?