Cov Lus Nyab Xeeb Lus Txhais Dhau Dhau Tag Nrho Cov Ntawv Nruab Nrab Ntaus Nrig
Lus Askiv Structured Query (SQL) yog cov lus ntawm databases. Tag nrho cov niaj hnub kev sib txuas lus databases , suav txog kev siv, FileMaker Pro, Microsoft SQL neeg rau zaub mov thiab Oracle siv SQL ua lawv lub tsev nrawm. Qhov tseeb, nws feem ntau tsuas yog tib txoj kev uas koj tuaj yeem cuam tshuam nrog lub database xwb. Tag nrho cov graphical neeg siv interfaces uas muab cov ntaub ntawv nkag teb chaws thiab manipulation functionality yog tsis muaj dab tsi ntau dua SQL neeg txhais lus. Lawv siv cov kev ua koj ua tau nrawm thiab hloov lawv kom SQL cov lus tau to taub los ntawm lub database.
SQL zoo li Lus Askiv
Nyob rau ntawm qhov no, tej zaum koj yuav xav hais tias koj tsis yog tus programmer thiab kawm ib hom lus programming tsis yog li koj tus cob qhia. Zoo hmoo, nyob rau hauv nws cov tub ntxhais, SQL yog ib hom lus yooj yim. Nws muaj tsawg tsawg tus commands, thiab cov lus txib yog nyeem tau heev thiab muaj cov txheej txheem zoo li cov kab lus Askiv.
Qhia cov Databases
Yuav kom nkag siab txog SQL, nws tseem ceeb heev kom muaj kev nkag siab yooj yim txog li cas cov database ua haujlwm. Yog tias koj nyiam nrog cov nqe lus xws li "rooj lus," "piv," thiab "lus nug," xav kom tau plough right tom ntej! Yog tias tsis yog, koj tuaj yeem nyeem cov lus Tshooj Database Fund ua ntej koj tsiv.
Cia peb saib ib qho piv txwv. Xav tias koj muaj ib cov lus qhia yooj yim uas tsim los khaws cov khoom muag rau lub khw muag khoom. Ib qho ntawm cov ntxhuav hauv koj cov ntaub ntawv yuav muaj cov nqi ntawm cov khoom ntawm koj lub tsev muag khoom los ntawm cov zauv cim uas qhia txog txhua yam khoom. Koj yuav zaum muab lub rooj ntawd lub npe yooj yim xws li "Nqi."
Tej zaum koj xav tshem tawm cov khoom ntawm koj lub khw uas muaj nqi tshaj $ 25, koj yuav "nug" tus database rau ib daim ntawv teev tag nrho cov khoom no.Qhov no yog qhov twg SQL los.
Koj thawj SQL lus nug
Ua ntej peb nkag mus rau hauv SQL daim ntawv yuav tsum tau muab cov lus qhia no, cia peb sim ua lus nug peb cov lus Askiv. Peb xav kom "xaiv txhua tus lej ntawm cov nqi ntawm qhov uas tus nqi yog tshaj $ 25." Qhov no yog ib qho yooj yim heev thaum hais hauv lus Askiv meej, thiab nws yog qhov yooj yim hauv SQL. Ntawm no yog qhov sib piv SQL daim ntawv qhia:
Xaiv TshawbNoj
LOS NTAWM Nqi
Qhov twg> 5
Nws yog ib qho yooj yim li ntawd! Yog tias koj nyeem cov lus hais saum toj no nrov nrov, koj yuav pom tias nws tsis zoo ib yam li lus Askiv uas peb tau hais rau hauv pawg lus kawg.
Txhais SQL Cov Lus Txhais
Tam sim no cia peb sim lwm tus yam ntxwv. Lub sij hawm no, txawm li ntawd los, peb mam li ua nws rov qab. Ua ntej, kuv mam li muab koj cov lus SQL thiab peb saib yog tias koj tuaj yeem piav txog nws hauv lus Askiv zoo:
Xaiv nqe
LOS NTAWM Nqi
Qhov twg yog StockNumber = 3006
Yog li, koj xav tias tsab ntawv no ua li cas? Yog, nws retrieves tus nqi ntawm cov database rau yam khoom 3006.
Muaj ib qhov kev qhia yooj yim uas koj yuav tsum tau muab ntawm peb qhov kev sib tham ntawm lub sij hawm no: SQL zoo li lus Askiv. Tsis txhob txhawj txog li cas koj tsim SQL lus; peb mam li mus hais tias nyob rau ntawm lawd peb cov ntawv. Xwb twb paub lawm hais tias SQL tsis yog kev ntshai li nws yuav xub tshwm sim.
Cov kab lus ntawm SQL Cov Lus
SQL muab ntau cov nqe lus, uas xaiv yog ib qho xwb. Nov yog qee cov qauv ntawm lwm cov lus SQL:
- SQL INSERT thiab SQL DELETE: Muab pov tseg los sis tshem tawm cov ntaub ntawv los ntawm lub rooj
- SQL Hloov tshiab: Kho cov ntaub ntawv hauv ib lub rooj
- SQL CREATE thiab SQL DROP: Tsim lossis tshem tawm ib lub rooj
Ntxiv rau cov lus SQL no, koj tuaj yeem siv SQL clauses, ntawm lawv qhov clause siv nyob hauv cov qauv ua piv txwv dhau los. Cov ntawv clauses no yog pab ua kom zoo ntawm cov ntaub ntawv los ua haujlwm. Ntxiv nrog rau qhov chaw ua hauj lwm, ntawm no yog lwm cov kev siv clauses:
- THIAB lossis LOSSIS: Muab ntau yam kev kho mob los ua kom zoo dua daim SQL
- LIKE: Sib piv cov nuj nqis rau cov kev ntseeg zoo sib xws uas siv cov tsiaj qus
- HAIS LUS: Saj cov ntaub ntawv nyob hauv nce lossis nqis los
Yog tias koj xav kawm ntxiv txog SQL, SQL Fundamentals yog ib feem ntau cov ntsiab lus uas tshawb cov qauv thiab sib nrauj ntawm SQL hauv ntau yam.