SQL Server 2012 - 使用 select 语句中的函数优化 SQL 查询

Question

有人对提高以下 select 语句的效率有什么建议吗？这是一个非常简单的查询，但是使用该代码的 SSRS 达到了超时设置。

SELECT   
   G.A
   ,B = IsNull(Avg(CAST(T.B as decimal)), 0)
   ,C = Sum(T.C)
   ,D = IsNull(Avg(CAST(T.D as decimal)), 0)
FROM 
   TableA as G 
INNER JOIN 
   TableB as T ON T.An_ID = G.An_ID
group by G.A

这是 SSRS 使用的 SP 的较大脚本中具有相同分组的代码片段。

Answer 1

对于此查询：

SELECT G.A, B = IsNull(Avg(CAST(T.B as decimal)), 0),
       C = Sum(T.C), D = IsNull(Avg(CAST(T.D as decimal)), 0)
FROM TableA G INNER JOIN 
     TableB T
     ON T.An_ID = G.An_ID
GROUP BY G.A;

您需要 TableB(An_ID) 和 TableA(An_Id, A) 上的索引。

我的猜测是连接产生了大量的中间行。您可以通过以下方式获得计数：

select sum(a.cnt * b.cnt)
from (select an_id, count(*) as cnt from tablea group by an_id) a join
     (select an_id, count(*) as cnt from tableb group by an_id) b
     on a.an_id = b.an_id;

你可以找到进攻组合：

select top 100 a.cnt * b.cnt, a.an_id
from (select an_id, count(*) as cnt from tablea group by an_id) a join
     (select an_id, count(*) as cnt from tableb group by an_id) b
     on a.an_id = b.an_id
order by a.cnt * b.cnt desc

SQL Server 2012 - 使用 select 语句中的函数优化 SQL 查询

SQL Server 2012 - Optimizing SQL query with functions in select statement

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sql-server-2012