Lus Askiv Structured Query Language (SQL) yog cov lus qhia uas siv los sib txuas nrog cov kev sib txuas lus database . Qhov tseeb, SQL yog tib hom lus uas feem ntau cov databases nkag siab. Thaum twg koj tuaj yeem nrog cov ntaub ntawv xws li, tus software txhais koj cov lus txib (seb lawv yog cov nas clicks lossis daim ntawv nkag) rau hauv SQL daim ntawv qhia tias cov ntaub ntawv paub txog kev txhais lus. SQL muaj peb lub ntsiab Cheeb Tsam: Cov Ntaub Ntawv Qhia Txog Manipulation (DML), Cov Lus Txhais Cov Lus Txhais (DDL), thiab Cov Ntaub Ntawv Qhia Txog Cov Ntaub Ntawv (DCL).
Hom siv ntawm SQL hauv Web
Raws li ib tug neeg siv ntawm txhua tus database-uas tau tsav software, koj yuav siv SQL, txawm tias koj tsis paub nws. Piv txwv, database-driven dynamic web page (zoo li feem ntau cov websites) yuav siv cov tswv yim los ntawm cov ntawv thiab clicks thiab siv nws los compose tus SQL lus nug uas retrieves cov ntaub ntawv los ntawm tus database yuav tsum ua kom tsim cov nplooj ntawv tom ntej.
Xav txog qhov piv txwv ntawm cov txheej txheem hauv online uas muaj kev tshawb nrhiav. Tshawb ntawm nplooj ntawv yuav muaj xws li ib daim ntawv uas muaj ib lub thawv ntawv uas koj nkag mus rau lub sij hawm nrhiav thiab ces nias lub khawm tshawb. Thaum koj nias lub khawm, lub web server tau txais cov ntaub ntawv los ntawm cov khoom database uas muaj lub sij hawm tshawb nrhiav thiab siv cov ntsiab lus los tsim cov nplooj ntawv web page rau koj qhov kev thov.
Piv txwv, Yog tias koj tshawb rau cov khoom uas muaj lub sij hawm "Irish," tus neeg siv yuav siv cov lus nram qab no rau SQL los muab cov khoom siv:
Txhais, cov lus txib no tau muab cov ntaub ntawv khaws tseg los ntawm cov ntaub ntawv lub npe hu ua "cov khoom" uas muaj cov cim "Irish" nyob rau hauv lub npe khoom.
Cov Ntaub Ntawv Qhia Txog Manipulation
Cov ntaub ntawv Manipulation Language (DML) muaj lub npe ntawm cov SQL commands feem ntau - cov uas tsuas muab cov ntsiab lus ntawm cov ntaub ntawv hauv ib daim ntawv. DML plaub xa cov ntaub ntawv los ntawm cov ntaub ntawv database (SELECT), ntxiv cov ntaub ntawv tshiab rau database (INSERT hais kom ua), hloov cov ntaub ntawv tam sim no muab khaws cia rau hauv ib qho database (UPDATE hais kom ua), thiab tshem tawm cov ntaub ntawv ntawm lub database DELETE hais kom ua).
Cov Lus Txhais Hom Lus
Cov Ntaub Ntawv Txhais Lus (DDL) muaj cov lus txib uas tsawg dua. DDL commands hloov cov qauv tseeb ntawm lub database, ntau dua li cov ntaub ntawv database. Piv txwv ntawm feem ntau siv DDL cov lus qhia muaj xws li cov neeg siv los tsim cov ntaub ntawv tshiab database (CREATE TABLE), hloov cov qauv ntawm cov ntaub ntawv database (ALTER TABLE), thiab rho tawm cov ntaub ntawv database (DROP COV LUS).
Cov Ntaub Ntawv Qhia Txog Kev Tswj
Cov Ntaub Ntawv Qhia Txog Cov Ntaub Ntawv (DCL) yog siv los tswj cov neeg siv nkag mus rau cov chaw xa khoom siv . Nws muaj ob nqe lus txib: GRANT hais kom ua, siv ntxiv cov nplooj permissions rau tus neeg siv, thiab REVOKE hais kom ua, siv los tshem tawm cov kev cai uas twb muaj lawm. Cov lus txib ob no tsim cov tub ntxhais ntawm txoj kev ruaj ntseg database ruaj ntseg qauv.
Cov qauv ntawm kev hais kom ua SQL
Muaj hmoo rau cov neeg ntawm peb cov uas tsis yog cov neeg siv computer, SQL commands yog tsim los kom muaj ib qho syntax zoo ib yam lus Askiv. Lawv feem ntau pib nrog cov lus txib hais txog qhov kev nqis tes ua, ua raws li lub ntsiab lus uas piav txog lub hom phiaj ntawm kev hais kom ua (xws li cov lus teev nyob rau hauv cov ntaub ntawv hauv cov lus nug uas raug cuam tshuam los ntawm kev hais kom ua) thiab thaum kawg, ib co lus clauses uas muab cov lus qhia ntxiv.
Feem ntau, tsuas yog nyeem ntawv SQL tsab ntawv tawm suab nrov nrov yuav qhia rau koj ib lub tswv yim zoo heev ntawm qhov kev txib tau npaj ua. Siv ib pliag los nyeem qhov kev piv txwv ntawm SQL daim ntawv qhia:
Koj tuaj yeem twv seb tsab ntawv no yuav ua licas? Nws nkag mus rau ntawm tus neeg kawm ntawv lub rooj ntawm lub database thiab tshem tawm tag nrho cov ntaub ntawv rau cov tub ntxhais kawm ntawv uas kawm tiav hauv xyoo 2014.
Kawm SQL Programming
Peb 'lwm ntsia ntawm ob peb yoojyim piv txwv hauv SQL tsab ntawv no, tiam sis SQL yog cov lus siv lus dav thiab muaj zog heev. Rau ib qho kev qhia tob ntxiv, saib SQL Cov Ntsiab Lus .