CTE Recursion Performance

CTE全名是Common Table Expression,语法基础请参考MSDN文档:https://msdn.microsoft.com/zh-cn/library/ms175972.aspx

CTE Recursion诞生之时,着实让人惊艳了一把。被很多吃瓜群众以讹传讹之后,“慢”似乎成了CTE Recursion最大的原罪。

很多时候,用到CTE Recursion的场景,无非是千八百条的数据量,最大也不过万八千条,所以“慢”算不上个问题。直到前几天,一个群友问:500W的数据做CTE递归时,怎么做性能优化……

结论:

  1. 合理的索引会极大的提升CTE Recursion的性能;
  2. 根据实验结果猜测:Sql Server2016对CTE Recursion做了优化,缺失合理索引的前提下,性能有极大的提升(受测试样本影响,结果可能不准确。无论如何,索引可以帮到你)。

 

 

Talk is cheap,Show me the code!所以,原因如下图(样本数据:1W零1条^^):

 

拒绝耍流氓,测试代码如下: 

 1 IF OBJECT_ID('dbo.TestCte', 'U') IS NOT NULL
 2 DROP TABLE dbo.TestCte;
 3 GO
 4 CREATE TABLE dbo.TestCte
 5     (
 6       Id VARCHAR(10) NOT NULL ,
 7       ParentId VARCHAR(10) NULL
 8     );
 9 WITH    cte_001
10           AS (    SELECT   1 AS a UNION ALL
11                 SELECT   2 AS a UNION ALL
12                 SELECT   3 AS a UNION ALL
13                 SELECT   4 AS a UNION ALL
14                 SELECT   5 AS a UNION ALL
15                 SELECT   6 AS a UNION ALL
16                 SELECT   7 AS a UNION ALL
17                 SELECT   8 AS a UNION ALL
18                 SELECT   9 AS a UNION ALL
19                 SELECT   10 AS a )
20     INSERT  dbo.TestCte
21             ( Id, ParentId )
22             SELECT    RIGHT( '0000000000' + CAST ( T01.Id AS VARCHAR(10) ), 10 ) AS Id ,
23                     RIGHT( '0000000000' + CAST ( CEILING( T01.Id / 10 ) AS VARCHAR(10) ), 10 ) AS ParentId
24             FROM (
25                     SELECT  ROW_NUMBER() OVER ( ORDER BY cte_001.a ) AS Id
26                     FROM    cte_001
27                             CROSS JOIN cte_001 AS A
28                             CROSS JOIN cte_001 AS B
29                             CROSS JOIN cte_001 AS C
30                             CROSS JOIN cte_001 AS D
31                             CROSS JOIN cte_001 AS E
32                             CROSS JOIN (SELECT TOP 5 * FROM cte_001) AS F ) AS T01;
33 GO
34 
35 INSERT DBO.TestCte ( Id, ParentId )
36 VALUES  ( '0000000000',  NULL );
37 GO
View Code
 1 --无索引版本
 2 SET STATISTICS TIME ON;
 3 SET STATISTICS IO ON;
 4 
 5 IF OBJECT_ID('dbo.T', 'U') IS NOT NULL
 6 DROP TABLE dbo.T;
 7 GO
 8 CREATE TABLE dbo.T
 9     (
10       RN UNIQUEIDENTIFIER PRIMARY KEY,
11       Id VARCHAR(10) ,
12       ParentId VARCHAR(10) ,
13       Memo1 NVARCHAR(128) DEFAULT ( N'我是占位置的!我是占位置的!我是占位置的!我是占位置的!我是占位置的!' ) ,
14       Memo2 NVARCHAR(128) DEFAULT ( N'我是很骄傲的!我是很骄傲的!我是很骄傲的!我是很骄傲的!我是很骄傲的!' )
15     );
16 INSERT  dbo.T
17         ( RN ,
18           Id ,
19           ParentId
20         )
21         SELECT  N.RN ,
22                 N.Id ,
23                 N.ParentId
24         FROM    ( SELECT    NEWID() AS RN ,
25                             Id ,
26                             ParentId
27                   FROM      dbo.TestCte
28                   WHERE     Id < 10001--测试数据量,改这里
29                 ) AS N
30         ORDER BY RN ASC;
31 GO
32 WITH    cte_001
33           AS ( SELECT   Id ,
34                         ParentId
35                FROM     dbo.T
36                WHERE    ParentId IS NULL
37                UNION ALL
38                SELECT   T01.Id ,
39                         T01.ParentId
40                FROM     T AS T01
41                         INNER JOIN cte_001 AS T02 ON T02.Id = T01.ParentId
42              )
43     SELECT  COUNT(*)
44     FROM    cte_001;
View Code
 1 --有索引版本
 2 SET STATISTICS TIME ON;
 3 SET STATISTICS IO ON;
 4 IF OBJECT_ID('dbo.T', 'U') IS NOT NULL
 5 DROP TABLE dbo.T;
 6 GO
 7 CREATE TABLE dbo.T
 8     (
 9       RN UNIQUEIDENTIFIER PRIMARY KEY,
10       Id VARCHAR(10) ,
11       ParentId VARCHAR(10) ,
12       Memo1 NVARCHAR(128) DEFAULT ( N'我是占位置的!我是占位置的!我是占位置的!我是占位置的!我是占位置的!' ) ,
13       Memo2 NVARCHAR(128) DEFAULT ( N'我是很骄傲的!我是很骄傲的!我是很骄傲的!我是很骄傲的!我是很骄傲的!' )
14     );
15 INSERT  dbo.T ( RN , Id , ParentId )
16         SELECT  N.RN , N.Id , N.ParentId
17         FROM    ( SELECT    NEWID() AS RN , Id , ParentId
18                   FROM      dbo.TestCte
19                   WHERE     Id < 10001--测试数据量,改这里
20                 ) AS N
21         ORDER BY RN ASC;
22 GO
23 
24 --创建索引
25 CREATE NONCLUSTERED INDEX IDX_DBO_T_PARENTID_ID
26 ON [dbo].[T] ([ParentId], Id)
27 GO
28 
29 WITH    cte_001
30           AS ( SELECT   Id , ParentId
31                FROM     dbo.T
32                WHERE    ParentId IS NULL
33                UNION ALL
34                SELECT   T01.Id , T01.ParentId
35                FROM     T AS T01
36                         INNER JOIN cte_001 AS T02 ON T02.Id = T01.ParentId
37              )
38     SELECT  COUNT(*)
39     FROM    cte_001;
View Code

 

posted @ 2016-10-15 21:49  羊汤大饼  阅读(129)  评论(0编辑  收藏  举报