SQL Query for sorting and getting unique count

I have a table which consists of the following details

Customer	Deal	DealStage
A	D1	Lost
A	D2	Won
A	D3	Contacted
B	D4	Conatcted
B	D5	Lost
C	D6	Lost
D	D7	Lost

I have to develop a query where I should get the unique highest stage for each customer. The Stage priority is Won > Contacted > Lost. For Example, A is having three deals which are Won, Lost, and Contacted. So I should be considering Won. Similarly Contacted for B and Lost for C and D

Is it possible to get an Output like

Customer	Highets Stage
A	Won
B	Contacted
C	Lost
D	Lost

By this, I can generate a pivot table that looks like

Stage	CustomerCount
Won	1
Contacted	1
Lost	2

Thanks in Advance

Answer

One option uses aggregation and field():

select customer,
    case min(field(deal_stage, 'Won', 'Contacted', 'Lost'))
        when 1 then 'Won'
        when 2 then 'Contacted'
        when 3 then 'Lost'
    end as highest_stage
from mytable
group by customer

Actually we could combine this with elt():

select customer,
    elt(
        min(field(deal_stage, 'Won', 'Contacted', 'Lost')), 
        'Won', 'Contacted', 'Lost'
    ) as highest_stage
from mytable
group by customer

You can then generate the final result with another level of aggregation:

select highest_stage, count(*)
from (
    select customer,
        elt(
            min(field(deal_stage, 'Won', 'Contacted', 'Lost')), 
            'Won', 'Contacted', 'Lost'
        ) as highest_stage
    from mytable
    group by customer
) t
group by highest_stage