COUNT () OVER (PARTITION BY) and DISTINCT - response (1) by dnoeth

Hi Gwen,
SELECT DISTINCT is processed after the OPAP function and COUNT(DISTINCT)  can't be used in OLAP, but in this case you don't need it, just GROUP BY first:

SELECT
    name
    , hair_colour
    , COUNT(hair_colour) OVER (PARTITION BY name)
FROM
    MyTable
GROUP BY 
    name
    , hair_colour;

Dieter