正文

SQL Server ->> Computed Column（计算列）

IP云
IP云V管理员/3 阅读
06/20
小程序：扫一扫查出行
【扫一扫了解最新限行尾号】
复制小程序

Computed Column（计算列）是自SQL Server 2005开始就有的特性。计算列的定义是一个表达式。表达式可以是非计算列，常量，函数间的组合。但是不可以是子查询。

计算列数据固化

默认情况下计算列的数据是存储在磁盘上，仅当计算列被查询引用是才进行实时计算。只在计算列在定义是添加了PERSISTED关键词是才将数据固化。

计算列上创建索引或者作为分区函数的引用列

计算列上是运行创建索引和作为分区函数的引用列。但是必须指定PERSISTED关键词。

用法其实很简单。那么这里有些问题。使用计算列的代价到底有多大？

INSERT发生时使用计算列和非计算列的性能区别

这里做一个测试。首先创建好两张表

IF EXISTS(SELECT * FROM sys.tables WHERE name = 'computed_column_test_computed')
BEGIN
DROP TABLE dbo.computed_column_test_computed
ENDIF EXISTS(SELECT * FROM sys.tables WHERE name = 'computed_column_test_noncomputed')
BEGIN
DROP TABLE dbo.computed_column_test_noncomputed
ENDCREATE TABLE dbo.computed_column_test_computed
(
dttm DATETIME,
dttm_year AS YEAR(dttm) PERSISTED,
dttm_month AS MONTH(dttm) PERSISTED,
dttm_nextday AS DATEADD(DAY,1,dttm) PERSISTED,
dttm_previousday AS DATEADD(DAY,-1,dttm) PERSISTED,
dttm_week AS DATEPART(ww,dttm),
dttm_monthname AS CASE DATEPART(mm, dttm)
WHEN 1 THEN 'January'
WHEN 2 THEN 'February'
WHEN 3 THEN 'March'
WHEN 4 THEN 'April'
WHEN 5 THEN 'May'
WHEN 6 THEN 'June'
WHEN 7 THEN 'July'
WHEN 8 THEN 'August'
WHEN 9 THEN 'September'
WHEN 10 THEN 'October'
WHEN 11 THEN 'November'
WHEN 12 THEN 'December'
END PERSISTED,
dttm_quarter AS DATEPART(qq,dttm) PERSISTED
)CREATE TABLE dbo.computed_column_test_noncomputed
(
dttm DATETIME,
dttm_year SMALLINT,
dttm_month SMALLINT,
dttm_nextday DATETIME,
dttm_previousday DATETIME,
dttm_week INT,
dttm_monthname VARCHAR(30),
dttm_quarter VARCHAR(30)
)

然后开启IO和TIME的统计信息开关，然后分别对两张表进行数据插入。

SET STATISTICS TIME ON
SET STATISTICS IO ONINSERT dbo.computed_column_test_computed(
dttm
)
SELECT DATEADD(SECOND, Num, GETDATE())
FROM dbo.Numbers
WHERE Num <= 1000000INSERT dbo.computed_column_test_noncomputed(dttm ,
dttm_year ,
dttm_month ,
dttm_nextday ,
dttm_previousday ,
dttm_week ,
dttm_monthname ,
dttm_quarter)
SELECT GETDATE(),
YEAR(GETDATE()) PERSISTED,
MONTH(GETDATE()) PERSISTED,
DATEADD(DAY,1,GETDATE()) ,
DATEADD(DAY,-1,GETDATE()),
DATEPART(ww,GETDATE()),
CASE DATEPART(mm, GETDATE())
WHEN 1 THEN 'January'
WHEN 2 THEN 'February'
WHEN 3 THEN 'March'
WHEN 4 THEN 'April'
WHEN 5 THEN 'May'
WHEN 6 THEN 'June'
WHEN 7 THEN 'July'
WHEN 8 THEN 'August'
WHEN 9 THEN 'September'
WHEN 10 THEN 'October'
WHEN 11 THEN 'November'
WHEN 12 THEN 'December'
END,
DATEPART(qq,GETDATE())
FROM dbo.Numbers
WHERE Num <= 1000000

我的例子里面分别进行10万行、30万行、50万行和100万行数据的插入测试。一共有7个计算列。每个例子测试两次。

SQL Server Execution Times:
CPU time = 0 ms, elapsed time = 0 ms.
Table 'computed_column_test_computed'. Scan count 0, logical reads 100840, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 164, physical reads 2, read-ahead reads 162, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 515 ms, elapsed time = 1564 ms.(100000 row(s) affected)SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 1327 ms.
Table 'computed_column_test_noncomputed'. Scan count 0, logical reads 100833, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 164, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 265 ms, elapsed time = 759 ms.(100000 row(s) affected)SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 5 ms. SQL Server Execution Times:
CPU time = 0 ms, elapsed time = 0 ms. SQL Server Execution Times:
CPU time = 0 ms, elapsed time = 0 ms.
Table 'computed_column_test_computed'. Scan count 0, logical reads 100840, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 164, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 391 ms, elapsed time = 411 ms.(100000 row(s) affected)
Table 'computed_column_test_noncomputed'. Scan count 0, logical reads 100833, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 164, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 234 ms, elapsed time = 273 ms.(100000 row(s) affected) SQL Server Execution Times:
CPU time = 0 ms, elapsed time = 0 ms.
SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 6 ms.
Table 'computed_column_test_computed'. Scan count 0, logical reads 302521, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 487, physical reads 1, read-ahead reads 330, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 1250 ms, elapsed time = 1986 ms.(300000 row(s) affected)
SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 74 ms.
Table 'computed_column_test_noncomputed'. Scan count 0, logical reads 302499, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 487, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 813 ms, elapsed time = 966 ms.(300000 row(s) affected)SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 14 ms.
Table 'computed_column_test_computed'. Scan count 0, logical reads 302521, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 487, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 1156 ms, elapsed time = 1709 ms.(300000 row(s) affected)
Table 'computed_column_test_noncomputed'. Scan count 0, logical reads 302499, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 487, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 734 ms, elapsed time = 3089 ms.(300000 row(s) affected)SQL Server parse and compile time:
CPU time = 8 ms, elapsed time = 8 ms.
Table 'computed_column_test_computed'. Scan count 0, logical reads 504201, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 809, physical reads 0, read-ahead reads 315, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 2031 ms, elapsed time = 2080 ms.(500000 row(s) affected)
Table 'computed_column_test_noncomputed'. Scan count 0, logical reads 504166, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 809, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 1297 ms, elapsed time = 2915 ms.(500000 row(s) affected)SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 0 ms.
SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 4 ms.
Table 'computed_column_test_computed'. Scan count 0, logical reads 504201, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 809, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 1984 ms, elapsed time = 3540 ms.(500000 row(s) affected)
SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 2 ms.
Table 'computed_column_test_noncomputed'. Scan count 0, logical reads 504166, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 809, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 1266 ms, elapsed time = 1341 ms.(500000 row(s) affected)SQL Server parse and compile time:
CPU time = 13 ms, elapsed time = 13 ms.
Table 'computed_column_test_computed'. Scan count 0, logical reads 1008359, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 1615, physical reads 0, read-ahead reads 791, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 4500 ms, elapsed time = 9110 ms.(1000000 row(s) affected)
Table 'computed_column_test_noncomputed'. Scan count 0, logical reads 1008333, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 1615, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 2531 ms, elapsed time = 3903 ms.(1000000 row(s) affected)SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 0 ms.
SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 3 ms.
Table 'computed_column_test_computed'. Scan count 0, logical reads 1008359, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 1615, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 3797 ms, elapsed time = 6559 ms.(1000000 row(s) affected)
SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 3 ms.
Table 'computed_column_test_noncomputed'. Scan count 0, logical reads 1008333, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 1615, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 2422 ms, elapsed time = 3895 ms.(1000000 row(s) affected)

可以看到确实使用computed column会对性能有一定的影响。当计算列数量越多的情况下性能的影响越大。但是当计算列数量很少的情况下，影响或者说差别其实很小很小。以我做的实验为例，讲计算列数量减少到只有3个，数据量依旧停留在100万行的情况，两者的性能差异其实已经很小了。

SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 4 ms. SQL Server Execution Times:
CPU time = 0 ms, elapsed time = 0 ms. SQL Server Execution Times:
CPU time = 0 ms, elapsed time = 0 ms.
Table 'computed_column_test_computed'. Scan count 0, logical reads 1005813, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 1615, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 3203 ms, elapsed time = 5058 ms.(1000000 row(s) affected)
Table 'computed_column_test_noncomputed'. Scan count 0, logical reads 1005319, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 1615, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 2281 ms, elapsed time = 4747 ms.(1000000 row(s) affected)SQL Server parse and compile time:
CPU time = 16 ms, elapsed time = 28 ms.
Table 'computed_column_test_computed'. Scan count 0, logical reads 1005813, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 1615, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 2984 ms, elapsed time = 3512 ms.(1000000 row(s) affected)
Table 'computed_column_test_noncomputed'. Scan count 0, logical reads 1005319, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 1615, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times:
CPU time = 2672 ms, elapsed time = 2859 ms.(1000000 row(s) affected)

那么总结下，计算列的使用原则我认为是在表中计算列的数量本身不多，而且一次性数据行插入量不大，计算逻辑固定，计算复杂度大的情况下，推荐使用计算列。

比如像DimDate这种表，表中可能有非常多的属性列用于表示当前日期的一些额外属性，比如下一天的日期，前一天的日期等等。用计算列是一个很好的选择。

参考：

Computed Columns

SQL Server ->> Computed Column（计算列）的更多相关文章

  1. SQL Server中的标识列

    一.标识列的定义以及特点 SQL Server中的标识列又称标识符列,习惯上又叫自增列. 该种列具有以下三种特点: .列的数据类型为不带小数的数值类型 .在进行插入(Insert)操作时,该列的值是由 ...

  2. SQL Server自动化运维系列——关于邮件通知那点事（&period;Net开发人员的福利）

    需求描述 在我们的生产环境中,大部分情况下需要有自己的运维体制,包括自己健康状态的检测等.如果发生异常,需要提前预警的,通知形式一般为发邮件告知. 邮件作为一种非常便利的预警实现方式,在及时性和易用性 ...

  3. SQL Server自动化运维系列——监控跑批Job运行状态（Power Shell）

    需求描述 在我们的生产环境中,大部分情况下需要有自己的运维体制,包括自己健康状态的检测等.如果发生异常,需要提前预警的,通知形式一般为发邮件告知. 在上一篇文章中已经分析了SQL SERVER中关于邮 ...

  4. SQL SERVER将某一列字段中的某个值替换为其他的值 分类： MSSQL 2014-11-05 13&colon;11 67人阅读 评论&lpar;0&rpar; 收藏

    SQL SERVER将某一列字段中的某个值替换为其他的值 UPDATE 表名 SET 列名 = REPLACE(列名 ,'贷','袋') SQL SERVER"函数 replace 的参数 ...

  5. SQL Server 2016：内存列存储索引

    作者 Jonathan Allen,译者 谢丽 SQL Server 2016的一项新特性是可以在“内存优化表(Memory Optimized Table)”上添加“列存储索引(Columnstor ...

  6. SQL Server -&gt&semi;&gt&semi; ColumnStore Index（列存储索引）

    Columnstored index是SQL Server 2012后加入的重大特性,数据不再以heap或者B Tree的形式存储(row level)存储在每一个数据库文件的页里面,而是以列为单位存 ...

  7. Sql Server中的标识列&lpar;自增长字段&rpar;

    一.标识列的定义以及特点 SQL Server中的标识列又称标识符列,习惯上又叫自增列.该种列具有以下三种特点: 1.列的数据类型为不带小数的数值类型2.在进行插入(Insert)操作时,该列的值是由 ...

  8. SQL Server 2012 自动增长列，值跳跃问题

    介绍 从 SQL Server 2012 版本开始, 当SQL Server 实例重启之后,表格的自动增长列的值会发生跳跃,而具体的跳跃值的大小是根据增长列的数据类型而定的.如果数据类型是 整型(in ...

  9. 为SQL Server表中的列添加&sol;修改&sol;删除注释属性（sp&lowbar;addextendedproperty、sp&lowbar;updateextendedproperty、sp&lowbar;dropextendedproperty）

    本篇基本完全参考:sql--sp_addextendedproperty和sp_updateextendedproperty (Transact-SQL) 三个存储过程用法一样,以sp_addexte ...

随机推荐

  1. java基础 集合类

    java集合类主要有以下集中: List结构的集合类: ArrayList类, LinkedList类, Vector类, Stack类 Map结构的集合类: HashMap类,Hashtable类 ...

  2. codeforces 744C Hongcow Buys a Deck of Cards

    C. Hongcow Buys a Deck of Cards time limit per test 2 seconds memory limit per test 256 megabytes in ...

  3. bigworld源码分析（3）——dbMgr分析

    dbMgr主要是玩家数据的读取和保存的,例如在bigworld源码分析(3)中,玩家在认证的时候,loginApp需要通过dbMgr来验证玩家数据是否合法,这就是针对玩家的账号数据进行查询.本篇中,我 ...

  4. MYSQL数据库函数集合

    一.数学函数 ABS(x)   返回x的绝对值 BIN(x)   返回x的二进制(OCT返回八进制,HEX返回十六进制) CEILING(x)   返回大于x的最小整数值 EXP(x)   返回值e( ...

  5. 从VS转MyEclipse的15天使用体验

    脱离了VS强大的IDE功能之后,转向MyEclipse,发现很大差别,Java的IDE对比VS感觉弱很多,而且树形没有那么好用,Java里面是以包为主,区别与C#的最大就是,高亮提示关键字,这一点Ja ...

  6. Python每日一练&lpar;1&rpar;&colon;计算文件夹内各个文章中出现次数最多的单词

    #coding:utf-8 import os,re path = 'test' files = os.listdir(path) def count_word(words): dic = {} ma ...

  7. cocos2d-x 3&period;0 rapidJson 解析操作应该注意的细节

    Size visibleSize = Director::getInstance()->getVisibleSize(); Point origin = Director::getInstanc ...

  8. &period;Net Core 学习资料

    官方网站:https://www.microsoft.com/net/core#windows   官方文档:https://docs.asp.net/en/latest/intro.html   中 ...

  9. （11&period;28）Java小知识！

    关于继承的继承机制:继承中最常使用的两个关键字是exteds和implements.今天主要和大家分享extends的知识点.这两个关键字的使用决定了一个对象和另一个对象是否是IS-A关系.同时我们还 ...

  10. OO第一次作业总结

    OO第一次学习总结 1.第一次作业:多项式加法 从未接触过java的我,在从输入输出开始学了几天后,按照C语言的思路,写出了一个与面向过程极其接近的程序. 在这个程序中,存在两个类:一个是Comput ...