mysql查询以获取表中特定字段的百分比？

Question

我有一张费用表：

Expense(amount: Double, vendorId: Int, vendorType: Int)

我想创建一个mysql查询，它将给出每个供应商类型与特定供应商的百分比，例如：

vendorId   vendorType percentOfExpencesOfThisType    totalExpenses

因此，假设我有4个经验：

Expense(amount: 30.0, vendorId: 3, vendorType: 1)
Expense(amount: 58.5, vendorId: 3, vendorType: 1)
Expense(amount: 47.0, vendorId: 3, vendorType: 7)
Expense(amount: 21.5, vendorId: 3, vendorType: 13)

因此该表将如下所示：

vendorId   vendorType percentOfExpencesOfThisType    totalExpenses
3               1                 50                       4
3               7                 25                       4
3               13                25                       4

我该怎么做呢？(很遗憾，使用的是mysql 5.6版)

Answer 1

您可以使用聚合函数和窗口函数：

select vendorId, vendorType,
       100 * count(*) / sum(count(*)) over (partition by vendorId) as percentOfExpensesOfThisType,
       sum(count(*)) over (partition by vendorId) as totalExpenses
from expense
group by vendorId, vendorType;

从MySQL 8+开始，可以使用窗口函数。

在早期版本中，您将联接两个聚合查询：

select vendorId, vendorType,
       100 * vt.cnt / v.cnt as percentOfExpensesOfThisType,
       v.cnt as totalExpenses
from (select vendorId, vendorType, count(*) as cnt
      from expense
      group by vendorId, vendorType
     ) vt join
     (select vendorId, count(*) as cnt
      from expense
      group by vendorId
     ) v
     on vt.vendorId = v.vendorId;