MsSql教程网-SQL Server 2008 新特性 总结复习一

1. TVP, 表变量,临时表,CTE 的区别

TVP和临时表都是可以索引的,总是存在tempdb中,会增加系统数据库开销,而表变量和CTE只有在内存溢出时才会被写入tempdb中。对于数据量大,并且反复使用,反复进行查询关联的,建议使用临时表或TVP,数据量小,使用表变量或CTE比较合适

2. sql_variant 万能类型

可以存放所有数据类型,相当于C#中的object数据类型

3. datetime, datetime2, datetimeoffset

datetime 时间有效期较小,在1753-1-1 之前就不能使用了,精度为毫秒级别,而datetime2 数据范围相当于C#中的datetime ,精度达到了秒后面小数点后7位,datetimeoffset则是考虑是时区的日期类型

4. MERGE的用法

语法很简单就不说了,主要是处理两张表某些字段对比后的操作,需注意 when not matched (by target) 与 when not matched by source的区别,前者是是针对对比后目标表不存在的记录,可以选择insert操作,而后者则是针对对比后目标表多出来的记录,可以选择delete或update操作

5. rowversion 类型

代替以前的timestamp,时间戳,8字节二进制值,常用来进行解决并发操作的问题

6. Sysdatetime()

返回datetime2类型,精度比datetime高

7. with cube , with rollup , grouping sets 运算符

都可与group by 后连用,with cube 表示汇总所有级别的组合,with rollup 则是按级别汇总,从下面的代码可以详细看出区别。注意,汇总行,null可以看成所有值

而grouping sets运算符,则仅返回每个分组顶级汇总行,在查询汇总行中 可使用grouping(字段名) = 1来判断,该运算符可和rollup, cube连用,表示按照grouping by sets和按照rollup/cube处理的结果集union all

示例代码如下:


复制代码 代码如下:

With cube, With rollup

–示例代码

declare @t table(goodsname VARCHAR(max) ,sku1name VARCHAR(max) , sku2name VARCHAR(max), qty INT)

insert @t select ‘凡客TX’,’红色’,’S’,1

insert @t select ‘凡客TX’,’黑色’,’S’,2

insert @t select ‘凡客TX’,’白色’,’L’,3

insert @t select ‘京东村山’,’白色’,’L’,4

insert @t select ‘京东村山’,’红色’,’S’,5

insert @t select ‘京东村山’,’黑色’,’L’,6

insert @t select ‘亚马逊拖鞋’,’白色’,’L’,7

insert @t select ‘亚马逊拖鞋’,’红色’,’S’,8

SELECT * FROM @t

select goodsname,sku1name,sku2name,sum(qty) sumqty

from @t

group by goodsname,sku1name,sku2name with rollup

ORDER BY goodsname,sku1name,sku2name

select goodsname,sku1name,sku2name,sum(qty) sumqty

from @t

group by goodsname,sku1name,sku2name with cube

ORDER BY goodsname,sku1name,sku2name

———————–

declare @t table(goodsname VARCHAR(max) ,sku1name VARCHAR(max) , sku2name VARCHAR(max), qty INT)

insert @t select ‘凡客TX’,’红色’,’S’,1

insert @t select ‘凡客TX’,’黑色’,’S’,2

insert @t select ‘凡客TX’,’白色’,’L’,3

insert @t select ‘京东村山’,’白色’,’L’,4

insert @t select ‘京东村山’,’红色’,’S’,5

insert @t select ‘京东村山’,’黑色’,’L’,6

insert @t select ‘亚马逊拖鞋’,’白色’,’L’,7

insert @t select ‘亚马逊拖鞋’,’红色’,’S’,8

–GROUPING SETS 运算符

SELECT goodsname,sku1name,sku2name, SUM(qty) FROM @t GROUP BY GROUPING SETS(goodsname,sku1name,sku2name)

SELECT goodsname, sku1name, sku2name ,SUM(qty) FROM @t

GROUP BY GROUPING SETS(goodsname), ROLLUP(sku1name,sku2name)

ORDER BY goodsname,sku1name,sku2name

SELECT goodsname, sku1name, sku2name ,SUM(qty) FROM @t

GROUP BY ROLLUP(goodsname,sku1name,sku2name)

ORDER BY goodsname,sku1name,sku2name

SELECT CASE WHEN GROUPING(goodsname) = 1 THEN ‘[ALL]’ ELSE goodsname END goodsname,

CASE WHEN GROUPING(sku1name) = 1 THEN ‘[ALL]’ ELSE sku1name END sku1name,

CASE WHEN GROUPING(sku2name) = 1 THEN ‘[ALL]’ ELSE sku2name END sku2name ,SUM(qty) FROM @t

GROUP BY GROUPING SETS(goodsname), ROLLUP(sku1name,sku2name)

ORDER BY goodsname,sku1name,sku2name

8. 一些快捷的语法 例如 Declare @id int = 0

虽然有时很快捷,但DBA不建议这样使用,Declare @id = select top 1 id from 表名,建议声明和查表赋值分开

9. 公用表达式 CTE

特点:可嵌套使用,代替联接表中的子查询,结构层次更加清晰,也可用来递归查询,另外通过巧妙的常量列控制递归层次

示例代码如下:


复制代码 代码如下:

使用CTE

–公用表达式CTE Common table expression

–用CTE实现递归算法

CREATE TABLE EMPLOYEETREE(

EMPLOYEE INT PRIMARY KEY,

employeename nvarchar(50),

reportsto int

)

insert into EMPLOYEETREE values(1,’Richard’,null)

insert into EMPLOYEETREE values(2,’Stephen’,1)

insert into EMPLOYEETREE values(3,’Clemens’,2)

insert into EMPLOYEETREE values(4,’Malek’,2)

insert into EMPLOYEETREE values(5,’Goksin’,4)

insert into EMPLOYEETREE values(6,’Kimberly’,1)

insert into EMPLOYEETREE values(7,’Ramesh’,5)

———————-

–确定哪些员工向Stephen报告的递归查询

with employeeTemp as

(

select EMPLOYEE, employeename, reportsto from EMPLOYEETREE where EMPLOYEE = 2

union all

select a.EMPLOYEE, a.employeename, a.reportsto from EMPLOYEETREE as a

inner join employeeTemp as b on a.reportsto = b.EMPLOYEE

)

select * from employeeTemp where EMPLOYEE <> 2 –option(maxrecursion 2)

–不报错设置级联关联递归

with employeeTemp as

(

select EMPLOYEE, employeename, reportsto,0 as sublevel from EMPLOYEETREE where EMPLOYEE = 2

union all

select a.EMPLOYEE, a.employeename, a.reportsto,sublevel+1 from EMPLOYEETREE as a

inner join employeeTemp as b on a.reportsto = b.EMPLOYEE

)

select * from employeeTemp where EMPLOYEE <> 2 and sublevel <=2 –option(maxrecursion 2)

10. pivot 与 unpivot

前者用在行转列,注意:必须用聚合函数与PIVOT一起使用,计算聚会时将不考虑出现在值列中的任何空值;一般情况下,可以用列上的子查询来替换pivot语句,但是这样做效率不高

后者用在列转行,注意:如果某些列中有null值,将会被过滤掉,不产生新行;语法上For前指定的新列,对应原表指定列名中的值,For后指定的新列对应原表指定列名中的标题的值

两者都有的共性:语法上最后必须要有别名;IN里面指定的列类型必须是一致的。

示例代码如下:


复制代码 代码如下:

pivot与unpivot

–关于PIVOT的操作

CREATE TABLE #test

(

NAME VARCHAR(max),

SCORE INT

)

INSERT INTO #test VALUES (‘张三’,’97’)

INSERT INTO #test VALUES (‘李四’,’28’)

INSERT INTO #test VALUES (‘王五’,’33’)

INSERT INTO #test VALUES (‘神人’,’78’)

–NAME SCORE

–张三 97

–李四 28

–王五 33

–神人 78

–行转列

SELECT –‘成绩单’ AS SCORENAME ,

[张三], [李四], [王五]

FROM #test

PIVOT (AVG(SCORE) FOR NAME IN ([张三], [李四], [王五])) b

—————————————–

CREATE TABLE VendorEmployee(

VendorId INT,

Emp1Order INT,

Emp2Order INT,

Emp3Order INT,

Emp4Order INT,

Emp5Order INT,

)

GO

INSERT INTO VendorEmployee VALUES(1,4,3,5,4,4)

INSERT INTO VendorEmployee VALUES(2,4,1,5,5,5)

INSERT INTO VendorEmployee VALUES(3,4,3,5,4,4)

INSERT INTO VendorEmployee VALUES(4,4,2,5,4,4)

INSERT INTO VendorEmployee VALUES(5,5,1,5,5,5)

SELECT * FROM VendorEmployee

—————-

–列转行

SELECT * FROM (

SELECT VendorId,[Emp1Order],[Emp2Order],[Emp3Order],[Emp4Order],[Emp5Order] FROM VendorEmployee) AS unpiv

UNPIVOT (orders FOR elyid IN ([Emp1Order],[Emp2Order],[Emp3Order],[Emp4Order],[Emp5Order])) AS child

ORDER BY elyid

SELECT * FROM VendorEmployee

UNPIVOT (orders FOR elyid IN ([Emp1Order],[Emp2Order],[Emp3Order],[Emp4Order],[Emp5Order])) AS child

ORDER BY elyid

SELECT * FROM VendorEmployee UNPIVOT ( ORDERS FOR [操作员名字] IN ([Emp1Order],[Emp2Order],[Emp3Order],[Emp4Order],[Emp5Order]))

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