SQL Server 總結(jié)復(fù)習(xí)(一)

更新時(shí)間：2012年08月09日 22:12:47 作者：

寫這篇文章，主要是總結(jié)最近學(xué)到的一些新知識(shí)，這些特性不一定是SQLSERVER最新版才有，大多數(shù)是2008新特性，有些甚至是更早。如果有不懂的地方，建議大家去百度谷歌搜搜，本文不做詳細(xì)闡述，有錯(cuò)誤的地方，歡迎大家批評(píng)指正

1. TVP，表變量，臨時(shí)表，CTE 的區(qū)別
TVP和臨時(shí)表都是可以索引的，總是存在tempdb中，會(huì)增加系統(tǒng)數(shù)據(jù)庫(kù)開(kāi)銷，而表變量和CTE只有在內(nèi)存溢出時(shí)才會(huì)被寫入tempdb中。對(duì)于數(shù)據(jù)量大，并且反復(fù)使用，反復(fù)進(jìn)行查詢關(guān)聯(lián)的，建議使用臨時(shí)表或TVP，數(shù)據(jù)量小，使用表變量或CTE比較合適
2. sql_variant 萬(wàn)能類型
可以存放所有數(shù)據(jù)類型，相當(dāng)于C#中的object數(shù)據(jù)類型
3. datetime, datetime2, datetimeoffset
datetime 時(shí)間有效期較小，在1753-1-1 之前就不能使用了，精度為毫秒級(jí)別，而datetime2 數(shù)據(jù)范圍相當(dāng)于C#中的datetime ，精度達(dá)到了秒后面小數(shù)點(diǎn)后7位，datetimeoffset則是考慮是時(shí)區(qū)的日期類型
4. MERGE的用法
語(yǔ)法很簡(jiǎn)單就不說(shuō)了，主要是處理兩張表某些字段對(duì)比后的操作，需注意 when not matched (by target) 與 when not matched by source的區(qū)別，前者是是針對(duì)對(duì)比后目標(biāo)表不存在的記錄，可以選擇insert操作，而后者則是針對(duì)對(duì)比后目標(biāo)表多出來(lái)的記錄，可以選擇delete或update操作
5. rowversion 類型
代替以前的timestamp，時(shí)間戳，8字節(jié)二進(jìn)制值，常用來(lái)進(jìn)行解決并發(fā)操作的問(wèn)題
6. Sysdatetime()
返回datetime2類型，精度比datetime高
7. with cube , with rollup , grouping sets 運(yùn)算符
都可與group by 后連用，with cube 表示匯總所有級(jí)別的組合，with rollup 則是按級(jí)別匯總，從下面的代碼可以詳細(xì)看出區(qū)別。注意，匯總行，null可以看成所有值
而grouping sets運(yùn)算符，則僅返回每個(gè)分組頂級(jí)匯總行，在查詢匯總行中可使用grouping(字段名) = 1來(lái)判斷，該運(yùn)算符可和rollup, cube連用，表示按照grouping by sets和按照rollup/cube處理的結(jié)果集union all
示例代碼如下：

復(fù)制代碼代碼如下:

 
With cube, With rollup 
--示例代碼 
declare @t table(goodsname VARCHAR(max) ,sku1name VARCHAR(max) , sku2name VARCHAR(max), qty INT) 
insert @t select '凡客TX','紅色','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 '京東村山','白色','L',4 
insert @t select '京東村山','紅色','S',5 
insert @t select '京東村山','黑色','L',6 
insert @t select '亞馬遜拖鞋','白色','L',7 
insert @t select '亞馬遜拖鞋','紅色','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','紅色','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 '京東村山','白色','L',4 
insert @t select '京東村山','紅色','S',5 
insert @t select '京東村山','黑色','L',6 
insert @t select '亞馬遜拖鞋','白色','L',7 
insert @t select '亞馬遜拖鞋','紅色','S',8 
--GROUPING SETS 運(yùn)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. 一些快捷的語(yǔ)法例如 Declare @id int = 0
雖然有時(shí)很快捷，但DBA不建議這樣使用，Declare @id = select top 1 id from 表名，建議聲明和查表賦值分開(kāi)
9. 公用表達(dá)式 CTE
特點(diǎn)：可嵌套使用，代替聯(lián)接表中的子查詢，結(jié)構(gòu)層次更加清晰，也可用來(lái)遞歸查詢，另外通過(guò)巧妙的常量列控制遞歸層次
示例代碼如下：

復(fù)制代碼代碼如下:

 
--公用表達(dá)式CTE Common table expression 
--用CTE實(shí)現(xiàn)遞歸算法 
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) 
---------------------- 
--確定哪些員工向Stephen報(bào)告的遞歸查詢 
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) 
--不報(bào)錯(cuò)設(shè)置級(jí)聯(lián)關(guān)聯(lián)遞歸 
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 與 unpivot
前者用在行轉(zhuǎn)列，注意：必須用聚合函數(shù)與PIVOT一起使用，計(jì)算聚會(huì)時(shí)將不考慮出現(xiàn)在值列中的任何空值；一般情況下，可以用列上的子查詢來(lái)替換pivot語(yǔ)句，但是這樣做效率不高
后者用在列轉(zhuǎn)行，注意：如果某些列中有null值，將會(huì)被過(guò)濾掉，不產(chǎn)生新行；語(yǔ)法上For前指定的新列，對(duì)應(yīng)原表指定列名中的值，F(xiàn)or后指定的新列對(duì)應(yīng)原表指定列名中的標(biāo)題的值
兩者都有的共性：語(yǔ)法上最后必須要有別名；IN里面指定的列類型必須是一致的。
示例代碼如下：

復(fù)制代碼代碼如下:

 
pivot與unpivot 
--關(guān)于PIVOT的操作 
CREATE TABLE #test 
( 
NAME VARCHAR(max), 
SCORE INT 
) 
INSERT INTO #test VALUES ('張三','97') 
INSERT INTO #test VALUES ('李四','28') 
INSERT INTO #test VALUES ('王五','33') 
INSERT INTO #test VALUES ('神人','78') 
--NAME SCORE 
--張三 97 
--李四 28 
--王五 33 
--神人 78 
--行轉(zhuǎn)列 
SELECT --'成績(jī)單' AS SCORENAME , 
[張三], [李四], [王五] 
FROM #test 
PIVOT (AVG(SCORE) FOR NAME IN ([張三], [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 
---------------- 
--列轉(zhuǎn)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 [操作員名字] IN ([Emp1Order],[Emp2Order],[Emp3Order],[Emp4Order],[Emp5Order])) 