无法计算表中聚合的聚合

在这个例子中,不同的国家每个月都会生产一些商品,每个商品都有特定的颜色。我试着根据每个国家暖色调和冷色调月比值的标准差对国家进行分类。

date         country    colour
-------------------------------
2020-03-01   France     Blue
2020-03-01   UK         Red
2020-03-02   USA        Green
2020-03-03   Belgium    Red
2020-03-04   UK         Green

第一个计算出的度量值确定了所有暖色调或冷色调的项目:

WARM_COLOUR:
{INCLUDE [Colour]: SUM(If [Colour] = 'Red' or [Colour] = 'Orange' or [Colour] = 'Yellow' THEN 1 ELSE 0 END)}

COLD_COLOUR:
{INCLUDE [Colour]: SUM(If [Colour] = 'Blue' or [Colour] = 'Green' THEN 1 ELSE 0 END)}

然后,我计算暖色和冷色的比例:

WARM_COLD_RATIO
sum([WARM_COLOR]) / (sum([WARM_COLOUR]) + SUM([COLD_COLOUR]))

最后,我想计算每个国家这个比率的标准差,但这会产生一个误差:

{INCLUDE [Country]: STDEV([WARM_COLD_RATIO])}
                    ^^^^^ Error: argument to STDEV is already an aggregation and can't be aggregated further