Question

我需要在下面运行更大版本的SQL Server 2008查询（SELECT的42次重复，与下面显示的4次重复相对应）。在我看来，它并不是非常优化的，也是使用while循环的理想候选者，但经过数小时的搜索和尝试后，我无法使其工作。任何人都可以建议更优化的查询来完成我需要的工作吗？

由于

SELECT 
    t1.Occupied as "1", t2.Occupied as "2", 
    t3.Occupied as "3", t4.Occupied as "4"
FROM 
    (SELECT 
         COUNT(function_id) AS Occupied
     FROM 
         ev_functions 
     WHERE 
         room_id = 22 
         AND DATEADD(HOUR,3,GETDATE()) > from_date_time 
         AND GETDATE() < to_date_time 
         AND function_status_id = 6) t1,
    (SELECT 
         COUNT(function_id) AS Occupied
     FROM 
         ev_functions 
     WHERE 
         room_id = 1 
         AND DATEADD(HOUR,3,GETDATE()) > from_date_time 
         AND GETDATE() < to_date_time 
         AND function_status_id = 6) t2,
    (SELECT 
         COUNT(function_id) AS Occupied
     FROM 
         ev_functions 
     WHERE 
         room_id = 1 
         AND DATEADD(HOUR,3,GETDATE()) > from_date_time 
         AND GETDATE() < to_date_time 
         AND function_status_id = 6) t3,
    (SELECT 
         COUNT(function_id) AS Occupied
     FROM 
         ev_functions 
     WHERE 
         room_id = 1 
         AND DATEADD(HOUR,3,GETDATE()) > from_date_time 
         AND GETDATE() < to_date_time 
         AND function_status_id = 6) t4

Answer 1

在您的情况下，您正在多次访问Same表以进行一小组更改

将SUM与CASE一起使用，以避免出现这种情况，并提高可读性

sum(case when room_id = 1 then 1 else 0 end ) as room1,
sum(case when room_id = 22 then 1 else 0 end )..
.....
and so on
from ev_functions 
where  DATEADD(HOUR,3,GETDATE()) > from_date_time 
and GETDATE() < to_date_time 
and function_status_id = 6

使用WHILE循环优化多个选择

1 个答案: