tailieu t sql

7/31/2019 Tailieu t SQL

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Bi 2

NGN NG T-SQL

Mc tiu bi hc:

- Bit cc c im chnh ca ngn ng T-SQL- M t bin, kiu d liu, v cc ch thch trong T-SQL.- Tm hiu hm v biu thc trong T-SQL- M t ngn ng DML, DDL, DCL

I. Gii thiu ngn ng T-SQL

- Ngn ng SQL l ngn ng ph bin nht c s dng trong th gii CSDL.

- T-SQL l vic thc thi ngn ng truy vn cu trc chun ca Microsoft.

- Ngn ng T-SQL c th dng nh ngha bng, chn, xo, cp nht v truy cp d

liu trong bng.

- T-SQL l ngn ng kh mnh c cp n kiu d liu, i tng tm thi, cc th

tc h thng v cc th tc mrng.

- T-SQL cn c kh nng x l trn mu tin, x l c iu kin, iu khin giao tc, x lli v bit l.

1. Bin trong T-SQL

- Bin l mt i tng c th lu gi mt gi tr d liu. D liu c thc chuyn n

cu lnh T-SQL bng vic s dng bin cc b. Bin c thc phn thnh 2 loi: bin

cc b v ton cc.

a. Bin cc b:

Trong T-SQL bin cc bc to v c s dng cho vic lu tr tm thi trong khi

cu lnh SQL c thc hin. Tn ca bin cc b phi bt u vi du @

C php:


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DECLARE

{

@local_variable [AS] data_type

}

Trong :

@local_variable: xc nh tn ca bin, tn ca bin phi bt u vi 1 du @.

Data_type: l kiu d liuc nh ngha bi ngi s dng hoc h thng.

Cu lnh SET hoc SELECTc s dng gn gi trn cho bin cc b.

C php:

SET @local_variable=value

OR

SELECT @local_variable=value

V d:

DECLARE @empID int

SET @empID = 1

SELECT FirstName, LastName

FROM Employee

WHERE EmployeeID=@empID

b. Bin ton cc

Bin ton cc l bin c nh ngha v x l bi h thng. Bin ton cc trong SQL

Server c bt u vi 2 du @. Gi tr ca cc bin ny c thc truy lc bng cu

truy vn SELECT n gin.

V d:


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SELECT @@VERSION AS sqlServerVersionDetails

2. Kiu d liu trong T-SQL

Kiu d liu l mt thuc tnh nh ngha d liu m mt i tng c th cha. T-SQL

bao gm mt s kiu d liu cbn nh varchar, text, v int. Tt c cc d liuc lu

tr trong SQL Server phi tng thch vi mt trong cc kiu d liu cbn .

Cc i tng sau y c kiu d liu:

- Ct trong table v trong view- Tham s trong Stored Procedure- Bin- Hm T-SQL tr v mt hoc nhiu gi tr d liu ca mt kiu d liu xc nh.- Th tc c cu lnh return lun c kiu d liu integer.Kiu d liu Kch thc Min gi tr d liu lu gi

Cc kiu d liu dng s nguyn

Int 4 Bytes T -2.147.483.648 n +2.147.483.647

Smallint 2 bytes T -32.768 n +32.767

Tinyint 1 byte T 0 n 255

Bit 1 byte 0,1 hoc NULL

Cc kiu d liu dng s thp phn

Decimal,

Numeric

17 bytes T -10^38 n +10^38

Cc kiu d liu dng s thc

Float 8 bytes T -1.79E +308 n +1.79E +308

Real 4 bytes T -1.79E +308 n +1.79E +308

Cc kiu d liu dng chui c di c nh (fixed)


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Char N bytes T 1 n 8000 k t, mi k t l 1 bytes

Cc kiu d liu dng chui c di bin i (variable)

Varchar N bytes T 1 n 8000 k t, mi k t l 1 bytes

Text N bytes T 1 n 2.147.483.647 k t, mi k t l 1

bytes

Cc kiu d liu dng chui dng font ch Unicode (national)

Nchar 2*n bytes T 1 n 4000 k t, mi k t l 2 bytes

Nvarchar 2*n bytes T 1 n 4000 k t,mi k t l 2 bytes

Ntext 2*n bytes T 1 n 1.073.741.823 k t, mi k t l 2

bytes

Cc kiu d liu dng tin t

Money 8 bytes T -922.337.203.685.477.5808 n

+922.337.203.685.477.5807

Smallmoney 4 bytes T -214.748.3648 n +214.748.3647

Cc kiu d liu dng ngy v gi

Datetime 8 bytes T 1/1/1753 n 31/12/9999

Smalldatetime 4 bytes T 1/1/1900 n 6/6/2079

Cc kiu d liu dng chui nh phn (binary string)

Binary N bytes T 1 n 8000 bytes

Varbinary N bytes T 1 n 8000 bytes

Image N bytes T 1 n 2.147.483.647 bytes

3. Ghi ch trong T-SQL

Microsoft SQL Server h tr2 kiu ghi ch:

-- (double hyphens). V d:


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USE pubs

--bang Employee chua chi tiet cua nhan vien

--Cau lenh nay truy luc tat ca cc hng cua bang Employee

SELECT * FROM Employee

/*.*/ (forward slash-asterisk character pairs) V du:

/* bang Employee chua chi tiet cua nhan vien. Cau lenh nay truy luc

tat ca cac hang cua bang Employee */

SELECT * FROM Employee

II. Hm v biu thc trong T-SQLHm l mt tp ca cc cu lnh T-SQL c s dng thc hin mt vi tc v

Biu thc l s kt hp canh danh, gi tr v ton t.

1. Hm trong T-SQL

T-SQL bao gm mt s lng ln cc hm. Cc hm c th hu ch khi d liuc

tnh ton v c x l.

a. Cc hm tp hpCc hm tp hp nh SUM, AVG, COUNT, MAX, MIN to ra cc gi tr tng hp

trong kt qu truy vn.

SQL Server h tr cc hm tp hp sau:

- SUMHm SUM tr v tng s ca tt c cc gi tr ca trng d liu trong biu thc. Ta

c th dng DISTINCT vi SUM tnh tng cho cc gi tr duy nht ca trng dliu trong biu thc. Cc gi tr NULL c b qua. SUM ch c th c dng vi

cc trng d liu kiu s (numeric).

C php: SUM(biu thc)


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V d: tm tng s hc vin ng k cho kho hc c CourseCode l 1 ta dng

hm SUM trong cu lnh SELECT nh sau:

SELECT SUM(NoOfStudentsEnrolled) AS Enrolled Students FROM Batch

WHERE CourseCode=1

Cc hm tp hp cn c ngha khc khi dng vi mnh GROUP BY. Chng ta

s bn v mnh GROUP BY trong phn sau.

- AVG

Hm AVG tr v gi tr trung bnh ca tt c cc gi tr ca trng d liu c ch ra

trong biu thc. AVG ch c th c dng vi cc trng s (numeric) v c th t

loi b cc gi tr NULL.

C php:

AVG ([ALL | DISTINCT] ) biu thc)

ALL: l gi tr mc nh, c tc dng vi tt c cc gi tr.

DISTINCT: Ch ra rng AVG ch lm vic vi mt gi tr duy nht ca trng cch ra, bt k cc gi tr ny xut hin bao nhiu ln.

Biu thc: c th l bt k biu thc SQL Server no, thng l tn trng d liu.

V d: tm trung bnh gi tr cc ho n trong bng Invoice ta dng cu truy vn

sau:

SELECT AVG(Amount) AS Average Amount FROM Invoice;

- COUNT

Hm COUNT m c cc gi tr khc NULL trong biu thc. Nu dng vi t

kho DISTINCT, COUNT m c cc gi tr duy nht. Hm COUNT c th c


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dng vi cc trng s v k t. Cc trng kho chnh v kho ngoi dng tt nht

vi hm COUNT v cc trng ny khng cha gi tr NULL.

Ta cng c th dng k t * thay cho biu thc trong hm COUNT. Vi cch dng

ny ta s m tt c cc mu tin m khng quan tm n bt k trng d liu no.

C php: COUNT (biu thc) hay COUNT(*)

V d: m s kho hc trong bng Course ta dng:

SELECT COUNT(CourseCode) AS Total Course FROM Course;

- MAX

Hm MAX tr v gi tr ln nht trong biu thc. Hm MAX c th c dng vi

cc kiu d liu s, chui, v ngy thng. MAX tr v gi tr ln nht trong ton b

gi tr sau khi i chiu. MAX b qua cc gi tr NULL.

C php: MAX(biu thc)

V d: tm gi tr ho n ln nht trong bng Invoice ta dng:

SELECT MAX(Amount) AS Maximum Invoice Amount FROM Invoice;

- MIN

Hm MIN tr v gi tr nh nht trong biu thc. Hm ny c th c dng vi cc

trng s, chui v ngy thng. Khi MIN c dng vi cc trng kiu chui, MIN

tr v gi tr nh nht trong danh sch so snh. MIN b qua gi tr NULL.

C php: MIN(biu thc)

V d: tm gi tr ho n nh nht trong bng Invoice ta dng truy vn sau:


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SELECT MIN(Amount) AS Minimum Invoice Amount FROM Invoice

b. Cc hm x l chui- Hm ASCII: hm tr v gi tr m ASCII ca k t bn tri ca chui.

V d:

Print ASCII(TOI)

Kt qu tr v nh sau:

84

- Hm char: hm ny chuyn i kiu m ASCII t s nguyn sang dng chui.V d:Print char(35)

Kt qu tr v nh sau:

#

- Hm UPPER: hm ny chuyn i chui sang kiu ch hoa.V d:

Print UPPER(Quyen)

Kt qu tr v nh sau:

QUYEN

- Hm LOWER: hm ny chuyn i chui sang kiu ch thng.V d:

Print LOWER(QUYEN)

Kt qu tr v nh sau:


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quyen

- Hm len: hmny tr v chiu di ca chui.V d:

Print len(Ly Tu Trong)

Kt qu tr v nh sau:

11

- Hm LTRIM: loi b khang trng bn tri ca chui.V d:

Print LTRIM( Trong)

Kt qu tr v nh sau:

Trong

- Hm RTRIM: loi b khong trng bn phi ca chui.V d:

Print RTRIM(LyTuTrong )

Kt qu tr v nh sau:

LyTuTrong

- Hm Left: tr v chui bn tri tnh t u cho n v tr th n.


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V d:

Print left(Quyen,3)

Kt qu tr v nh sau:

Quy

- Hm Right: tr v chui bn phi tnh t cui cho n v tr th n.V d:

Print Right(QUyen,4)

Kt qu tr v nh sau:

Uyen

- Hm CHARINDEX: tr v v tr chui bt u ca chui con trong chui xt.V d:

Print CHARINDEX(Trong,Ly Tu Trong)

Kt qu tr v nh sau:

7

c. Cc hm v x l thi gian- Hm getDate(): tr v ngy thng nm ca h thng

V d:

Select Today is =getDate()

Kt qu tr v nh sau:

Today is

2007-10-17 14:55:20

- Hm DATEPART: tr v mt phn gi tr ca mt chui dng ngy thng y .


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V d 1:

Select Hom nay ngay: =datepart(d,getDate())

Kt qu tr v nh sau:

Hom nay ngy:

17

V d 2:

Select Hom nay tuan: =datepart(w,getDate())

Kt qu tr v nh sau:

Hom nay tuan:

- - - - - - - - - - - - - - -

4

Hm ny bao gm cc h s nh trong bng sau:

Hm DATEPART Tham s

Year yy, yyyy

Quarter qq, q

Month mm, m

Dayofyear dy, y

Day dd, d

Week wk, ww

Weekday dw

Hour hh

Minute mi, n


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Second ss, s

Milecond ms

- Hm DATEDIFF: tr v s ngy trong khang thi gian gia ngy.V d:

Select So ngay giua ngay thu tien den hom nay: =datediff(d, ReceiptDate,

getDate())

From tblReceipt

Kt qu tr v nh sau:

So ngay giua ngay thu tien den hom nay:

- - - - - - - - - - - - - - - - - - -- - - -- - - - - - -

74

72

- Hm day: tr v ngy th my trong thng.V d:

Select Hom nay ngay: =day(getDate())

Kt qu tr v nh sau:

21

- Hm month: tr v thng th my trong nm.V d:

Select Hom nay thang:=month(getDate())

Kt qu tr v nh sau:

10


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- Hm year: tr v nmV d:

Select Nam nay la:=year(getDate())

Kt qu tr v nh sau:

2007

d. Cc hm v ton hc- Hm square: tr v bnh phng ca mt biu thc

V d:

Print square(4)

Kt qu tr v nh sau:

16

- Hm sqrt: tr v cn bc hai ca mt biu thc V d:

Print sqrt(4)

Kt qu tr v nh sau:

2

- Hm round: tr v s lm trn ca mt biu thc.V d:

Print round(748.58, -1)

Kt qu tr v nh sau:


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750.00

e. Cc hm v chuyn i- Hm cast: tr v gi tr c kiu d liu theo nh ngha

V d:

Print cast(getDate() as varchar(11))

Kt qu tr v nh sau:

Oct 17 2007

Kt qu bao gm 11 k t.

- Hm convert: chuyn i gi tr c kiu d liu ny sang kiu d liu khc nucho php.

V d:

Print convert(int, 12)

Kt qu tr v la s nguyn c gia tr nh sau:

12

Hoc chng ta c th dng hm ny ly thi gian t bin hay ct, gi tr c dng

ngy thng nh sau:

Print convert(char(10), getDate(), 108)

Kt qu tr v nh sau:

12 : 07 : 46

2. Biu thc trong T-SQL


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a. Biu thc iu kin

Nh chng ta bit T-SQL l mt tp hp ca vic lp trnh m rng t Microsoft. C

c th lp trnh cc chc nng trong CSDL quan h c cung cp bi SQL Server 2000.

Mnh WHERE c s dng nh mt phn ca mt cu lnh T-SQL lc dliu.Trong mnh WHERE thng s dng cc ton t so snh v cc biu thc iu

kin. Biu thc l s kt hp ca cc ton t v ton hng. Cc biu thc n gin c th

l mt bin n, hng n, ct n, Ton t c th c s dng kt hp 2 hay

nhiu biu thc n thnh mt biu thc phc tp.

Mt biu thc c th bao gm mt hay nhiu loi nh sau:

- Hng: th hin mt gi tr d liu n v gi tr d liu phi c th.- Ct: Tn ca ct trong mt bng. Ch tn ca ct c cho php trong mt biu

thc.

- Ton t mt ngi: Ton t ny ch c mt ton hng tham gia vo.- Ton t hai ngi: ton t ny nh ngha cch thc m 2 biu thc kt hp to ra

mt kt qu n. Ton t 2 ngi c th l mt ton t s hc, ton t gn (=), ton

t bitwise, ton t so snh, ton t logic,

Bng di y lit k cc ton t so snh c s dng trong cu lnh T -SQL trongmnh WHERE

Ton t M t

= Ton t bng

> Ln hn

< Nh hn

>= Ln hn v bng

Khng bng

! Ph nh


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V d:

PRICE >100

NAME LIKE DAVID

GRADE < > FAIL

Cc k t i din trong cu lnh T-SQL

K t i din M t V d

- Mt k t n SELECT udesc FROM

usertypes WHERE udesc

LIKE C_

% chiu di bt k mt chui SELECT * FROM users

WHERE username LIKE

AL%

[ ] Mt k t n trong phm vi mt

cp du ngoc vung

SELECT * FROM

coursematerial WHERE

yearsem LIKE SEM[1-2]

[ ^ ] Nhiu k t n m khng nm

trong phm vi cp du ngoc n.

SELECT * FROM

coursematerial WHERE

yearsem LIKE sem[^ 1-2]

b. Ton t lun l

Cc ton t lun l c h tr trong T-SQL l AND, OR, NOT

Cc ton t AND v OR c s dng gip tm kim cc iu kin trong mnh

WHERE. NOT l ton t ph nh. AND kt ni hai iu kin v tr v TRUE ch khi c

2 iu kin l TRUE. OR kt ni 2 iu kin nhng n ch tr v TRUE khi mt trong 2

iu kin l TRUE.

u tin ca ton t lun l l: NOT, AND, OR


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III. Ngn ng DDL

1. Cu lnh CREATE TABLE

Mt bng c th c to bng vic s dng mt trong 2 cch sau y:

- Enterprise Manager- Cc cu lnh T-SQL trong Query AnalyzerC php to bng bng T-SQL l:

CREATE TABLE

( )

V d:

CREATE TABLE SinhVien

( MSSV Char(4), HOTENSV varchar(15))

Chng ta c th to mt bng mi vi Enterprise Manager bng vic chn CSDL v

sau chn tu chn Action, New v Table.


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char(4) foreign key (MALOP) references LOP(MALOP)

)

- To rng buc Default trong khi to bngCREATE TABLE SINHVIEN

(

MSSV char(4), HOTEN varchar(20), NGAYSINH datetime, PHAI bit

DEFAULT 0

)

- To rng buc duy nht trong khi to bngCREATE TABLE SINHVIEN

(

MSSV char(4), HOTEN varchar(20), DIENTHOAI varchar(15) NOT

NULL UNIQUE

)

2. Cu lnh ALTER TABLE

- Lnh Alter table c s dng sa i vic nh ngha mt bng bng vic thay

i, thm, hoc xo cc ct v cc rng buc.

C php:

ALTER TABLE

ALTER COLUMN [ ] | ADD[ ] | DROP COLUMN []

V d 1:Thm ct DIACHI vo bng SINHVIEN

ALTER TABLE SINHVIEN


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ADD DIACHI varchar(20) NULL

V d 2:Thay i kiu d liu mi cho ct HOTEN ca bng SINHVIEN


ALTER COLUMN HOTEN nvarchar(30) NULL

V d 3:Xa ct DIACHI trong bng SINHVIEN


DROP COLUMN DIACHI

- To primary key cho ct trong bng tn tiALTER TABLE SINHVIEN

ADD CONSTRAINT PK_MSSV

PRIMARY KEY (MSSV)

- To rng buc kha ngoi trong bng tn tiALTER table SINHVIEN

Add constraint FK_MALOP

foreign key (MALOP) references LOP(MALOP)

- To rng buc check trong bng c d liuALTER table SINHVIEN

ADD CONTRAINT CK_NGAYSINH

CHECK (NGAYSINH


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DEFAULT 0 for PHAI

- To rng buc duy nht trong bng tn tiALTER TABLE SINHVIEN

( ADD CONSTRAINT UK_DIENTHOAI

UNIQUE(DIENTHOAI)

)

3. Cu lnh DROP TABLE

Cu lnh DROP TABLE xo vic nh ngha mt bng v tt c cc d liu, ch mc,

trigger, rng buc, v vic xc nh cc quyn cho bng .

C php:

DROP TABLE

V d:

DROP TABLE Employee

Ch :Cu lnh DROP TABLE khng th c dng xo mt bng m bng nyang c mi quan h vi bng khc. Trc khi xo phi quan tm n rng buc tham

chiu kho ngoi.

IV. Ngn ng DML v DCL

1. Cu lnh SELECT, INSERT, DELETE, UPDATE

a. Dng T-SQL InsertChng ta c th thm d liu mi vo mt bng hoc chng ta cng c th thm d liu

t mt bng ang tn ti vo mt bng mi c to ra.

C php cu lnh Insert thm d liu vo mt bng:

INSERT [INTO] VALUES

Trong :


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[INTO] l mt t kho

tn ca bng ni m record c chn vo.

xc nh cc gi tr cho ct ca bng.

V d:

Bng jobs bao gm 3

fields: job_desc, min_lvl, max_lvl.

C php thm d liu t mt bng vo mt bng khc

INSERT SELECT FROM

Trong : table name l tn ca bng ni m chng ta c th thm d liu vo , column

list l danh sch cc ct c chn vo t mt bng ang tn ti v tablename2 l tn ca

bng ang tn ti.

V d:

CREATE TABLE author_details (au_id varchar(11), au_lname varchar(40))

GO

INSERT author_details SELECT authors.au_id, authors.au_lname FROM authors

b. Dng T-SQL update

Chng ta c th thay i, cp nht d liu trong mt bng bng cu lnh UPDATE. Vic

cp nht th cn thit khi d liu cn c thay i.

C php cho vic cp nht mt hng n trong mt bng:

UPDATE

SET

[WHERE ]

Tham s c gii thch nh sau:

l tn ca bng ni m mu tin c cp nht.

INSERT INTO jobs VALUES (Graphics Artist, 25, 100)


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xc nh cc gi tr mi cho cc ct c thay i.

UPDATE titles SET price=price+(25/100*price) WHERE title_id=TC7777

Cp nht nhiu hng ca mt bng

UPDATE publishers

SET city=Atlanta, state=GA

c. Dng T-SQL delete:

C php xo mt hng t mt bng

DELETE FROM [WHERE ]

Trong :

l tn ca bng cha mu tin mun xo.

mnh WHERE c s dng xc nh iu kin

V d :

DELETE FROM pub_info WHERE pub_id=9999

d. Dng T-SQL SELECT:

C 5 phn c bn trnh by mt cu lnh SELECT n gin:

C php:

SELECT FROM ;

Trong :

- SELECT l t u tin trong cu query.- phi l thnh phn k tip trong cu query. Nu mun truy lc

t 2 hay nhiu ct trong cu SELECT th cc columnname phi c cch nhau

bi du chm v cc ct phi tn ti trong bng m chng ta ang truy lc.

- FROM phi l t k tip trong cu query ca chng ta.- l tn bng m chng ta ang truy lc.


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- Du ; l thnh phn cui cng trong cu query. Du ; ni cho SQL bit rngcu query hon thnh v by gi nn thc thi.

Cu lnh SELECT c thng dch nh sau:

SELECT (ci g?) Mt hay nhiu tn ct . Tn ct phi c tch rabi du phy. Ch rng tn ct cui cng khng

c du phy i km.

FROM (u?) Tn bng.

SELECT * FROM

SELECT c nhiu chc nng. Chng ta ch va nhn thy mt dng c bn m thi.

C mt scc chc nng khc nh sau:

- WHERE:y l mt phn ty chn ca query. Phn ny xc nh mt iu kin.Nu mt query khng c mnh WHERE th tt c cc hng trong bng s c

hin th. Cu lnh so snh cng c th c xc nh trong mnh ny. V d:

hin th tn ca sinh vin khi bit m s sinh vin ta lm nh sau:

SELECT hosv

tensv FROM sinhvien WHERE masv=ltt200603;

- GROUP BY:y l mt chc nng khc ca cu query. N ch c s dngkhi kt qu ca query phi c nhm da trn iu kin. V d: nu chng ta

mun hin th thng tin ca sinh vin t nhng m s sinh vin khc nhau c

nhm li bng mnh GROUP BY nh sau:


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SELECT masv, hosv, tensv

FROM sinhvien

GROUP BY masv;

- ORDER BY: Chc nng ny ca cu query cho php sp xp cc hng theo tht. V d: nu chng ta mun hin th thng tin ca sinh vin c m s

ltt200603 trong bng sinhvien c sp xp theo h ca sinh vin, ta lm nh

sau:

SELECT * FROM sinhvien WHERE masv=ltt200603 ORDER BY hosv;

Cu lnh SELECT n gin

Cu lnh n gin nht th hin tt c cc ct trong mt bng c ghi nh sau:

SELECT * FROM sinhvien;

Cu lnh trn s hin th tt c cc hng v ct trong bng sinhvien. ct s hin th theo

th t nh ban u khi chng ta thit k bng.

Cc bng trong CSDL th thng ln v cha nhiu hng d liu. Tht vy, i lc chng

ta khng cn thit phi hin th tt c cc hng trong mt bng nh l kt qu ca cu

query trn. Chng ta c th s dng mnh WHERE lc cc d liu theo mt iu

kin cho trc.

iu kin c xc nh trong mnh WHERE c gi l mt thuc tnh. V d: Xt

cu query sau:

SELECT * FROM sinhvien WHERE phai=Nu;

Mnh WHEREc s dng gii hn kt qu ca query, ch hin th nhng bn

ghi c ct phi =Nu. Khi cu lnh c thc thi, mi mu tin trong bng s c so

snh vi gi tr trong iu kin. Ch nhng mu tin c gi tr tho mn iu kin mi


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SELECT masv, hosv, tensv, noisinh

FROM sinhvien

WHERE noisinh=TPHCM

ORDER BY masv;

Th t sp xp c th l tng dn hay gim dn. D ng cc tham s DESC hay ASC ta c

th sp xp cc mu tin theo th t yu cu. Nu khng c tham s no trong cu lnh

truy vn, th t sp xp l tng dn.

Ta c th kt hp cc trng d liu vi cc hng s kiu chui c kt qu d c v

nh dng hp l. Thng thng cc hng s ny khng tn ti nh mt trng d liutrong kt qu truy vn m c kt hp vi cc trng khc xy dng kt qu hin th

cho truy vn.

V d: thm vo cc k t : v -> trong kt qu truy vn d liu t bng titles ta

to truy vn nh sau:

SELECT title_id +: + title + -> +type

FROM titles;

Ch : khi dng ton t + trong danh sch truy vn, ta cn ch n kiu d liu ca cc

trng. Cc trng l ton hng ca ton t ny phi c cng kiu d liu, nu khng

SQL Server s bo li.

Mnh AS c th c dng thay i tiu ca trng d liu hay gn tiu cho

trng pht sinh trong kt qu ca cu truy vn. Cc trng hin th trong kt qu ca cu

truy vn thng c tiu l tn trng trong bng. c tiu d hiu hn ta dngmnh AS tu bin.

V d: hin th tiu ROLL NUMBER thay cho trng RollNo trong bng

Students ta dng cu lnh SELECT sau:


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SELECT RollNo AS ROLL NUMBER FROM Students

Cc cu lnh SELECT c th c dng vi cc rng buc.

V d: rng buc IDENTITY c th c s dng trong truy vn nh sau:

SELECT IDENTITY (datatype, seed, increment) AS ID_Number

INTO table2 FROM table1

Trong cu truy vn trn table1 l bng c sn v table2 l bng m ta mun to ra v a

cc gi tr t tng vo.

Datatype l kiu d liu ca trng t tng. Trng ny ch nhn cc kiu d liu integer

hay kiu d liu decimal.

Seed l gi tr gn cho mu tin u tin ca bng. Cc mu tin tip theo c gn cc gi

tr tng dn, cc gi tr ny c tnh bng tng cc gi tr IDENTITY cui cng cng

vi gi tr tng.

Increment l gi tr tng c cng thm cho cac mu tin tip theo ca bng d liu.

T kho DISTINCT loi b cc mu tin trng lp t truy vn. Nu khng c t kho

DISTINCT, truy vn s tr v tt c cc mu tin bao gm c cc mu tin trng lp.

V d: nu chng ta truy xut trng MaterialType trong bng Material khng dng

t kho DISTINCT ta s nhn c mt danh sch di cc gi tr MaterialType trng

lp. Nu dng DISTINCT trong truy vn SQL Server s ch tr v cc gi tr

MaterialType duy nht. Cu truy vn ny nh sau:

SELECT DISTINCT MaterialType FROM Material

Mnh TOPc dng hn ch s mu tin tr v trong kt qu truy vn.

Cu lnh SELECT ny c c php nh sau:

SELECT TOP n FROM

V d: hin th 3 mu tin u tin trong bng Students ta dng:


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SELECT TOP 3 * FROM Students

K t * trong cu truy vn truy xut tt c cc trng.

Tng t nh vy ta c th truy xut s mu tin theo t l phn trm t bng d liu.

V d:

SELECT TOP 40 PERCENT * FROM Students

s truy vn 40% mu tin u tin ca bng Students.

2. Cu lnh GRANT, REVOKE, DENY

a. Cu lnh GRANT

Cu lnh GRANT c s dng khi csd liuc chia s vi nhng ngi s

dng khc. Cu lnh GRANT c dng cp quyn truy cp d liu cho ngi s

dng.

C php:

GRANT

{ALL | statement [, .]}

ON table_name

TO Security_Account[, ]

Trong :

ALL chuyn tt c cc quyn cho i tng khi ALL c s dng cp quyn cho

ngi s dng trn mt i tng.

Statement cpn cu lnh m quyn c cho bi ngi s dng.

TO Security_Account xc nh quyn cho mt ngi s dng c bit no .

Ngi s dng c th l Microsoft SQL Server, mt SQL Server role, mt

Windows OS.

Table_name cp n tn ca bng m c cp quyn.


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V d:

GRANT SELECT ON Employee TO QUYEN

b. Cu lnh REVOKE

Cu lnh revoke c dng hu quyn ngi s dng c cp bi cu lnh grant

C php:

REVOKE

{ALL | statement[,]}

ON table_name

FROM Security_Account[,.]

V d:

REVOKE SELECT ON Employee FROM QUYEN

c. Cu lnh DENY

C php:

DENY

{ALL | statement[,]}

ON table_name

TO Security_Account[,.]

V d:

DENY SELECT ON Employee TO QUYEN

tailieu t sql

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