获取 main 中每个子组的计数

Question

我想获取出现在主组中的每个子组的计数。

鉴于以下情况：

| Clothing    | Colour
-----------------------
| Shirt       | black   
| Shirt       | black  
| Shirt       | black
| Shirt       | yellow 
| Shoes       | yellow
| Shoes       | yellow
| Shoes       | black

我想要的输出是：

| A                    | B
---------------------------
| Shirt_Blacks         | 3 
| Shirt_Yellows        | 1
| Shoes_Blacks         | 1
| Shoes_Yellows        | 2

编辑：输出格式 2：

| Clothing       | Black | Yellow
-----------------------------------
| Shirt          | 3     | 1
| Shoes          | 1     | 2

尝试了以下方法，但没有成功：

SELECT COUNT(Colour) 
FROM [randomtable]
Group By Clothing

Answer 1

使用聚合：

SELECT CONCAT(Clothing, '_', Colour) A, COUNT(*) B
FROM mytable
GROUP BY Clothing, Colour

Demo on DB Fiddle：

一个 |乙 :----------- | -： 衬衫_黑色 | 3 鞋_黑色 | 1 衬衫_黄色 | 1 鞋_黄色 | 2

---

如果您希望旋转结果集，那么：

SELECT 
    Clothing,
    SUM(CASE WHEN Colour = 'Black' THEN 1 ELSE 0 END) Black,
    SUM(CASE WHEN Colour = 'Yellow THEN 1 ELSE 0 END) Yellow
FROM mytable
GROUP BY Clothing

Answer 2

您可以按 concat(clothing, '_', colour) 分组：

SELECT
  concat(clothing, '_', colour) A, 
  COUNT(*) B
FROM [randomtable]
Group By concat(clothing, '_', colour) 

Answer 3

SELECT Clothing+'_'+Colour A, COUNT(*) B
    FROM [randomtable]
GROUP BY Clothing+'_'+Colour

select * from [randomtable]
    pivot
(count(colour) for colour in (black,yellow))AS piv