mysql查询以获取表中特定字段的百分比？

我有一份费用表：

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

我想创建一个mysql查询，该查询将为我提供特定供应商的每种供应商类型的百分比，如：

vendorId   vendorType percentOfExpencesOfThisType    totalExpenses

假设我有4项费用：

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，该表将显示：

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

我该怎么做？

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不幸的是，使用mysql 5.6版时，您可以使用聚合和窗口功能：

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;

可以从MySQL 8+开始使用窗口函数

在早期版本中，您将加入两个聚合查询：

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;

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不幸的是，使用mysql 5.6版时，您应该阅读@P.Salmon谢谢，我会阅读的。