Sql server sqlserver查询优化

我的问题是，我创建的查询执行时间太长

City   | Department  |  Employee   | Attendance Date | Attendance Status
------------------------------------------------------------------------
C1     | Dept 1      | Emp 1       | 2016-01-01      | ABSENT
C1     | Dept 1      | Emp 2       | 2016-01-01      | LATE
C1     | Dept 2      | Emp 3       | 2016-01-01      | VACANCY

因此，我想创建一个包含相同数据的视图，并添加一个包含员工总数的列（该列稍后在SSRS项目中用于确定每个状态的百分比）

因此，我创建了一个函数，可以根据部门和日期进行简单的选择过滤

这是使用函数的查询：

SELECT        City, Department, Employee, [Attendence Date], [Attendance Status], [Get Department Employees By Date](Department, [Attendence Date]) AS TOTAL
FROM            attendenceTable

CREATE FUNCTION [dbo].[Get Department Employees By Date]
(
    @deptID int = null,
    @date datetime = null
)
RETURNS nvarchar(max)
AS
BEGIN
    declare @result int = 0;
    select @result = count(*) from attendenceTable where DEPT_ID = @deptID and ATT_DATE_G = @date;
    RETURN @result;

END

这就是功能：

SELECT        City, Department, Employee, [Attendence Date], [Attendance Status], [Get Department Employees By Date](Department, [Attendence Date]) AS TOTAL
FROM            attendenceTable

CREATE FUNCTION [dbo].[Get Department Employees By Date]
(
    @deptID int = null,
    @date datetime = null
)
RETURNS nvarchar(max)
AS
BEGIN
    declare @result int = 0;
    select @result = count(*) from attendenceTable where DEPT_ID = @deptID and ATT_DATE_G = @date;
    RETURN @result;

END

问题是查询执行时间太长（我的意思是很长）。

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有什么优化建议吗？

您的函数是一个标量函数，对结果集中的每一行运行一次（~600000）次，是已知的性能杀手。可以将其重写为一个内联表值函数，或者如果其他地方不需要该逻辑，则一个简单的组count&join就足够了：

WITH    EmployeesPerDeptPerDate
          AS ( SELECT   DEPT_ID ,
                        ATT_DATE_G ,
                        COUNT(DISTINCT Employee) AS EmployeeCount
               FROM     attendenceTable
               GROUP BY DEPT_ID ,
                        ATT_DATE_G
             )
    SELECT  A.City ,
            A.Department ,
            A.Employee ,
            A.[Attendence Date] ,
            A.[Attendance Status] ,
            ISNULL(B.EmployeeCount, 0) AS EmployeeCount
    FROM    attendenceTable AS A
            LEFT OUTER JOIN EmployeesPerDeptPerDate AS B ON A.DEPT_ID = B.DEPT_ID
                                                            AND A.ATT_DATE_G = B.ATT_DATE_G;

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那个表中有什么索引？您通常如何过滤这些数据？请同时包括功能代码。数据经常变化吗？这能超过高峰之夜吗？数据库是MS SQL吗？你有索引吗？我只是想运行它以便继续我的工作，我等了将近一个半小时（该表有593236条记录）。@Garethleyons编辑后包含的代码：）