如何计算组的最大值？

Question

我有一个像这样的表（我不确定如何格式化表）

Category / Products / Purchases

1 | A | 12

1 | B | 13

1 | C | 11

2 | A | 1

2 | B | 2

2 | C | 3

预期输出：

1 | B | 13

2 | C | 3

但是我不断得到

1 | A | 13

2 | A | 3

即它只是选择第二列的第一次出现。这是我的代码：

SELECT Category, Products, MAX(Purchases) FROM myTable GROUP BY Category;

Answer 1

SELECT PRODUCTS,MAX(PURCHASES) AS MAXP FROM TABLE GROUP BY PRODUCTS

Answer 2

在where子句中使用过滤：

select t.*
from t
where t.purchases = (select max(t2.purchases) from t t2 where t2.category = t.category);

Answer 3

不存在：

select m.* from myTable m
where not exists (
  select 1 from myTable
  where category = m.category and purchases > m.purchases
)

请参见demo。结果：

| Category | Products | Purchases |
| -------- | -------- | --------- |
| 1        | B        | 13        |
| 2        | C        | 3         |