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Chng 2

Tng quan v c s d liu

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Ni dung

Cc khi nim ca CSDL quan h. Cc rng buc ton vn.

Chun ha d liu. Cc php ton i s quan h.

Ngn ng SQL.

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Cc khi nim ca CSDL quan h

C s d liu database

Csd liu l s tp hp c t chc cc dliu c lin quan lun l vi nhau.

D liu (data)

C t chc (organized) C lin quan lun l (logically related)

C s d liu quan h relational database

CSDL quan h l CSDL m d liu c lutr trong cc bng.

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Cc khi nim ca CSDL quan h

Mt s thut ngMin (domain)

Thuc tnh (attribute).

Lc quan h (relation schema).

V t (predicate) ca lc quan h.

Bc (degree) ca lc quan h.Quan h (relation).

Th hin quan h (relation instance).

B (tuple) ca quan h.

Bc (degree) ca quan h.

Kha (key) ca lc quan h.

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Cc khi nim ca CSDL quan h

Mt s thut ng Kha (key).

Kha d tuyn (candidate key).

Kha chnh (primary key).

Kha ngoi (foreign key).

Lc c s d liu (database schema). Rng buc ton vn (integrity constraint).

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Cc php ton i s quan h

Nm php ton c bn Php chn Php chiu Php hp Php hiu Php tch Descartes

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Cc php ton i s quan h

Cc php ton khc Php giao

Php kt Php kt t nhin Php kt ngoi Php na kt Php na kt t nhin Php chia

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nh ngha bng

C php ca lnh CREATE TABLE

CREATE TABLE []

AS SELECT statement;

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Thay i nh ngha bng

LnhALTER TABLEdng thay i nhngha ca mt bng.

C php ca lnh ALTER TABLE.ALTER TABLE

[ADD MODIFY DROP options]( [])

[ENABLE clause DISABLE clause];

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Hy b bng

Lnh DROP TABLE dng hy b mtbng trong mt lc .

C php ca lnh DROP TABLE:DROP TABLE [CASCADE CONSTRAINTS];

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Lnh INSERT

Thm d liu vo mt bng

C php ca lnh INSERT - Thm mt hng:

INSERT INTO [()]VALUES ();

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Lnh DELETE

Xa b cc hng ca mt bng

C php ca lnh DELETE:

DELETE [FROM]

[WHERE ];

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Lnh UPDATE

Cp nht d liu ca cc hng ca mtbng

C php ca lnh UPDATE:UPDATE []

SET = {, }

[, = {, } ][WHERE ];

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Lnh SELECT

Dng truy vn d liu ca mt bnghoc nhiu bng.

Lnh SELECTthc hin cc php ton cai s quan h. Php tch

Php kt Php chn Php chiu

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Lnh SELECT

C php ca lnh SELECT:SELECT [DISTINCT]

[INTO ]

FROM [WHERE ]

[GROUP BY

[HAVING ]][ORDER BY ];

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Lnh SELECT

Hnh 2.27. Th t x l ccmnh ca lnh SELECT.

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Hm kt hp

Hm kt hp (aggregate function) cnc gi l hm nhm (group function).

Hm Gi tr tr vAVG ([DISTINCT ALL] n) Gi tr trung bnh ca n, b qua cc gi tr

rng.

COUNT ([DISTINCT ALL S hng m exprc gi tr khc rng.* lm cho COUNT m tt c cc hngc chn, bao gm cc hng trng nhauv cc hng c gi tr rng.

] expr *)

Gi tr ln nht ca expr.MAX ([DISTINCT ALL] expr)Gi tr nh nht ca expr.MIN ([DISTINCT ALL] expr)Tng gi tr ca n, b qua cc gi tr rng.SUM ([DISTINCT ALL] n) lch chun (STanDard DEViation) ca n,b qua cc gi tr rng.

STDDEV ([DISTINCT ALL] n)Phng sai ca n, b qua cc gi tr rng.VARIANCE ([DISTINCT ALL] n)

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Cc php ton tp hp

Hai lnh SELECTc thc kt ni vinhau bng cc php ton tp hp bao gmphp hp (union), php giao (intersection)v php hiu (minus).

SELECT statement_1UNION [ALL]INTERSECTMINUSSELECT statement_2;

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X l gi tr rng

Hm NVL (Null VaLue) dng i gi trrng thnh mt gi tr khc rng.

Hm NVL c hai tham s: mt biu thc vmt gi tr khc rng.

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Truy vn con

Truy vn con subquery

L mt truy vn (lnh SELECT) nm trongmt truy vn khc.

Truy vn ngoi (outer query)

Truy vn trong (inner query) Truy vn chnh (main query)

Xut hin Trong iu kin ca mnh WHERE. Nh l mt bng trong mnh FROM.

Trong iu kin ca mnh HAVING.

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Truy vn con

Cc loi truy vn con Truy vn con lng nhau (nested subquery)

Truy vn con tng quan (correlatedsubquery)