表值函数中的条件 WHERE 子句

Question

我有一个表值函数

    CREATE FUNCTION [dbo].[DateRange] 
    (
        @StartDate date,
        @EndDate date,
        @Location varchar(25),
        @Device varchar(25)
    ) 
    RETURNS TABLE 
    AS
    RETURN 
    (
        SELECT *
        FROM MyTable
        WHERE Date < @EndDate AND
              Date > @StartDate AND
              Location = @Location AND
              Device = @Device 

    );

现在我想让用户选择使用 NULL 作为位置参数和/或设备参数，以便他/她获取与位置和设备无关的所有数据

什么是最优雅和最有效的方式来做到这一点？

Answer 1

就像这样：

CREATE FUNCTION [dbo].[DateRange] 
    (
        @StartDate date,
        @EndDate date,
        @Location varchar(25) = NULL,
        @Device varchar(25) = NULL
    ) 
    RETURNS TABLE 
    AS
    RETURN 
    (
        SELECT *
        FROM MyTable
        WHERE 
          Date < @EndDate 
          AND Date > @StartDate 
          AND ( @Location IS NULL OR (@Location IS NOT NULL AND Location = @Location))
          AND ( @Device IS NULL OR (@Device IS NOT NULL AND Device = @Device ))

    )

如果device和location列实际上可以为 NULL，您可能需要考虑此选项：

CREATE FUNCTION [dbo].[DateRange] 
    (
        @StartDate date,
        @EndDate date,
        @Location varchar(25) = NULL,
        @Device varchar(25) = NULL
    ) 
    RETURNS TABLE 
    AS
    RETURN 
    (
        SELECT *
        FROM MyTable
        WHERE 
          Date < @EndDate 
          AND Date > @StartDate 
          AND ( @Location IS NULL OR Location = @Location)
          AND ( @Device IS NULL OR Device = @Device )

    )

如果您在该位置使用 UD 表类型，这将有效，正如您在评论中所询问的那样。只需确保输入参数为只读即可。但是，您不能将 NULL 传递给表类型参数，您必须传递该类型的空参数对象：

CREATE TYPE LocationsType AS TABLE 
( LocationName VARCHAR(25));

CREATE TABLE MyTable (Date datetime, Location varchar(25), Device varchar(25));

CREATE FUNCTION [dbo].[DateRange] 
    (
        @StartDate date,
        @EndDate date,
        @Location LocationsType READONLY,
        @Device varchar(25) = NULL
    ) 
    RETURNS TABLE 
    AS
    RETURN 
    (
        SELECT *
        FROM MyTable
        WHERE 
          Date < @EndDate 
          AND Date > @StartDate 
          AND ( ((select count(*) FROM @Location) = 0) OR Location IN (select LocationName from @Location))
          AND ( @Device IS NULL OR Device = @Device )

    )

叫它：

declare @l LocationsType

select *
from [dbo].[DateRange] (getDate(), GetDate(), @l,NULL)