使用CTE解决复杂查询的问题

最近，同事需要从数个表中查询用户的业务和报告数据，写了一个SQL语句，查询比较慢：

Select 
S.Name,
S.AccountantCode,
(
Select COUNT(*) from (
Select Distinct BusinessBackupId from Biz_BusinessBackupCustomer where Id in (
Select BusinessBackupCustomerId from Rpt_RegistForm where ( SignatureCPA1Id=S.Id or SignatureCPA2Id=S.Id  ) and DocStatus=30  
) ) T 
) as 'BNum',
(case when R.Id is null then 0 else 1 end ) as 'Num', 
R.ReportBackupDate 
from 
Base_Staff S 
left join Rpt_RegistForm R on  (  R.SignatureCPA1Id=S.Id or R.SignatureCPA2Id=S.Id )  and R.DocStatus=30 
where S.UserType=3

该查询需要执行10秒左右，仔细分析，它有2次查询类似的结果集（Base_Staff,Rpt_RegistForm 关联部分），这正是CTE应用的场合。

从SQLSERVER 联机丛书，我们来了解下CET的概念：

ms-help://MS.SQLCC.v10/MS.SQLSVR.v10.zh-CHS/s10de_6tsql/html/27cfb819-3e8d-4274-8bbe-cbbe4d9c2e23.htm

指定临时命名的结果集，这些结果集称为公用表表达式 (CTE)。该表达式源自简单查询，并且在单条 SELECT、INSERT、UPDATE、MERGE 或 DELETE 语句的执行范围内定义。该子句也可用在 CREATE VIEW 语句中，作为该语句的 SELECT 定义语句的一部分。公用表表达式可以包括对自身的引用。这种表达式称为递归公用表表达式。

下面看看经过CET改写过的查询：

With CTE as
(
select 
       --s.Id as S_ID,
       s.Name ,s.AccountantCode,
       r.BusinessBackupCustomerId --, r.Id as R_ID ,r.SignatureCPA1Id,r.SignatureCPA2Id
from   Base_Staff  S 
left join  Rpt_RegistForm   R 
       on  (  R.SignatureCPA1Id=S.Id or R.SignatureCPA2Id=S.Id ) and r.DocStatus=30 
where s.UserType=3 

)
select t0.*
,(
  Select COUNT(*)  from (
    Select Distinct BusinessBackupId 
    from Biz_BusinessBackupCustomer b
    inner join CTE on b.Id =CTE.BusinessBackupCustomerId
    where t0.AccountantCode=CTE.AccountantCode
) t1
) as '约定书数'
from 
(
select Name, AccountantCode,COUNT( BusinessBackupCustomerId) as '报告数'
from CTE
group by Name,AccountantCode
) t0