问题描述

我有一些复杂的函数，我想在多个查询中使用它们.它获取一些值列表并返回聚合值.

I have some complex function that I want to use in number of queries. It gets some list of values and return aggregate value.

例如(我简化了，实际上更复杂):

For example (I simplify it, it is more complex in deed):

CREATE FUNCTION Mean(@N Numbers READONLY)
RETURNS TABLE AS RETURN (
    SELECT mean = SUM(n.value) / COUNT(*) FROM @N n
)

我想在查询中使用它:

SELECT d.DepartmentName, MeanRate = m.mean
FROM Departments d
CROSS APPLY Mean(
    (
        SELECT value = e.Rate
        FROM Employees e
        WHERE e.DepatmentId = d.DepatmentId
    )
) m

但我收到一个错误:操作数类型冲突:浮点数与数字不兼容

But I get an error: Operand type clash: float is incompatible with Numbers

我知道我可以使用游标或将值作为 XML 传递，但我认为这种方式比内联函数和表变量慢.

I know that I can use cursor or pass values as XML, but I think this ways are slower than inline function and table variables.

如何将值列表传递给内联函数?

How can I pass a list of values to inline function?

推荐答案

首先你应该使用 Inline 函数中使用的 table type(Number) 创建一个 table 变量.

First you should create a table variable using the table type(Number) used in the Inline function.

将需要的行插入表变量并传递表变量 o 内联函数

Insert the required rows into table variable and pass the table variable o Inline function

你需要做这样的事情

declare @Numbers Numbers

Insert into @Numbers 
select e.Rate
From Employees  E join 
Departments d on e.DepatmentId = d.DepatmentId

select * from Mean(@Numbers)

更新:根据您的评论

创建一个新的表格类型.

CREATE TYPE Dept_number AS TABLE
(
DepatmentId  INT ,value numeric(22,6)
);

Alter 函数

ALTER FUNCTION Mean(@dept_number DEPT_NUMBER readonly) 
returns TABLE 
AS 
    RETURN 
      (SELECT depatmentid, 
              mean = Sum(n.value) / Count(*) 
       FROM   @dept_number n 
       GROUP  BY depatmentid) 

调用函数

DECLARE @dept_number DEPT_NUMBER 

INSERT INTO @dept_number 
            (depatmentid, 
             value) 
SELECT d.depatmentid, 
       e.rate 
FROM   employees E 
       JOIN departments d 
         ON e.depatmentid = d.depatmentid 

SELECT * 
FROM   Mean(@dept_number) 

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