Nrhiav Tshaj Tawm Txog Database Views
Database views pub koj yooj yim txo cov complexity ntawm qhov kawg neeg siv thiab txwv lawv muaj peev xwm mus saib tau cov ntaub ntawv muaj nyob rau hauv cov ntaub ntawv database los ntawm limiting cov ntaub ntawv uas tau hais rau cov neeg siv kawg. Yeej tseem zoo nkauj, qhov pom siv cov lus nug ntawm cov lus nug ntawm database rau dynamically populate tus txheem ntawm cov ntaub ntawv database cov ntaub ntawv.
Vim Li Cas Siv Views?
Muaj ob qho laj thawj los muab cov neeg siv rau cov ntaub ntawv los ntawm cov kev xav es tsis muab lawv nrog kev nkag tau mus rau cov rooj database:
- Views muab yooj yim, granular kev ruaj ntseg . Koj tuaj yeem siv qhov kev pom zoo los txwv cov ntaub ntawv uas tus neeg siv tau pom hauv lub rooj. Piv txwv, yog tias koj muaj ib tus neeg ua hauj lwm rooj thiab xav kom muab qee cov neeg siv cov ntaub ntawv ntawm cov neeg ua hauj lwm puv sij hawm, koj tuaj yeem tsim kom pom tias tsuas yog cov ntaub ntawv. Qhov no yog qhov yooj yim dua qhov kev qhia (tsim thiab tswj tus duab ntxoov ntxoo lub rooj) thiab ua kom pom tseeb ntawm cov ntaub ntawv.
- Views ua kom yooj yim rau tus neeg siv kev paub . Views hide qhov ntsiab lus ntawm koj tus ntxhuav database ntawm kawg cov neeg siv uas tsis xav pom lawv. Yog tias ib tug neeg siv cov txheej txheem ntawm qhov saib, lawv yuav tsis pom lub rooj txhua kab uas tsis tau xaiv los ntawm qhov pom thiab lawv tsis to taub. Qhov no tiv thaiv lawv ntawm qhov tsis meej pem tshwm sim los ntawm lub npe tsis zoo, txhua tus cim tshwj xeeb thiab cov lus tuav .
Tsim Tus Saib
Tsim kom muaj kev pom zoo yog ncaj nraim: koj tsuas xav tsim cov lus nug uas muaj cov kev txwv koj xav kom tswj thiab muab tso rau hauv cov lus CREATE VIEW. Ntawm no yog cov syntax:
NPAJ KEEB KWM Saib
Piv txwv li, yog tias koj xav tsim cov neeg ua hauj lwm puv hnub uas kuv tau tham hauv seem dhau los, koj yuav muab cov lus txib nram qab no:
TSWV YIM TSHAJ NO
Xaiv thawj firstname, last_name, worker_id
LOS NTAWM cov neeg ua haujlwm
QHOV CHAW NYOB QHOV TWG = 'FT'
Hloov Saib
Hloov cov ntsiab lus ntawm qhov kev siv siv tib lub caij nyoog syntax li cov creation ntawm ib tug saib, tab sis koj siv lub ALTER lo lus txib hloov ntawm qhov kev txiav txim siab CREATE. Piv txwv li, yog tias koj xav ntxiv kev txwv rau kev saib xyuas tas hnub uas ntxiv tus neeg ua hauj lwm tus xov tooj rau cov txiaj ntsig, koj yuav muab cov lus txib nram qab no:
ALTER VIEW fulltime AS
Xaiv first_name, last_name, worker_id, xov tooj
LOS NTAWM cov neeg ua haujlwm
QHOV CHAW NYOB QHOV TWG = 'FT'
Muab Lub Saib
Nws yooj yim heev los tshem tawm cov kev pom los ntawm ib tug database siv DROP VIEW lus. Piv txwv, yog tias koj xav rho tawm cov neeg ua hauj lwm puv hnub, koj yuav siv cov lus txib nram qab no:
TAG MUAG tas hnub