ULwimi oluCwangcisiweyo lweeNgxelo (SQL) lubekwe imiyalelo esetyenziselwa ukusebenzisana nesiseko sedatha . Enyanisweni, i-SQL yilwimi kuphela eyona nto yolwazi olubanzi oluqondayo. Naluphi na usebenzisana naloo datha, isofthiwe iguqulela imilayezo yakho (nokuba ingachani i mouse okanye ifom yefomu) kwisitatimende se-SQL ukuba isiseko sedatha siyakwazi ukutolika. I-SQL inezixhobo ezintathu eziphambili: uLwimi lokuLawulwa kweData (iDML), uLwimi lweNkcazo yeData (iDDL), kunye noLwazi loLawulo lweDatha (DCL).
Ukusetyenziswa ngokuqhelekileyo kweSQL kwiWebhu
Njengomsebenzisi weprogram yesofthiwe eqhutywe ngeenkcukacha, mhlawumbi usebenzisa iSQL, nokuba awukwazi. Ngokomzekelo, iphepha lewebhu elinamandla elinokwenziwa kwedata (njengamawebhusayithi amaninzi) lithatha igalelo lomsebenzisi kwiifom kunye kunye nokuchofoza kwaye ulisebenzise ukubhala umbuzo we-SQL ofumana ulwazi oluvela kwiziko elifunekayo ukuvelisa iphepha elilandelayo lewebhu.
Cinga ngomzekelo wekhathalogu elula kwi-intanethi kunye nomsebenzi wokukhangela. Ikhasi lokukhangela lingaba nefomu equlethe ibhokisi yombhalo apho ungena kwikota yophando uze uklikha iqhosha lokukhangela. Xa ukakraza iqhosha, umncedisi wewebhu ufumana nayiphi na irekhodi esuka kwisiseko semveliso equkethe ixesha lokukhangela kwaye isebenzisa iziphumo ukudala iphepha lewebhu elithile kwisicelo sakho.
Umzekelo, ukuba uphendule iimveliso eziqulethe igama elithi "i-Irish," umncedisi angasebenzisa isitatimende esilandelayo seSQL ukufumana iimveliso ezihambelana nazo:
Uguqulelwe, lo myalelo ufumana nayiphi na irekhodi esuka kwitheyibhile yedatha ebizwa ngokuthi "iimveliso" eziqulethwe ngabalinganiswa "zitshintshile" naphi na phakathi kwegama lomkhiqizo.
ULwimi lokuLawulwa koLwazi
ULwimi lokuLawulwa kweData (DML) luqulethe i-subset yemiyalelo ye-SQL esetyenziswe rhoqo - leyo elula nje ukuqulethe okuqukethwe kwidatha ngolunye uhlobo. Iimilazo ezine eziqhelekileyo zeDML zifumana ulwazi oluvela kumgca-siseko (UMSEBENZI), faka ulwazi olutsha kwisiseko sedatha (umyalelo we-INSERT), guqula ulwazi olugcinwe kwisiseko sedatha (umyalelo we-UPDATE), ususe ulwazi kwiziko ledatha ( SUSELA umyalelo).
Iinkcazelo zeeLwimi
ULwimi lweNkcazelo yeDatha (iDDL) luqulethe imithetho engasetyenziswa rhoqo. Imithetho yeDDL iguqula isakhiwo esona senkcukacha, kunokuba isiseko se-database. Imimiselo yemiyalelo yeDDL esetyenziswa ngokuqhelekileyo ibandakanya ezo zisetyenziselwa ukuvelisa ithebula leenkcukacha elitsha (DALA ITHEBHU), guqula isakhiwo setafile yedatha (ALTER TABLE), kwaye ususe itafile yedatha (DROP TABLE).
ULwimi loLawulo lweDatha
ULwimi loLawulo lweDatha (DCL) lisetyenziselwa ukulawula ukufikelela komsebenzisi kwiinkcukacha zolwazi . Iqulethe imiyalelo emibini: umyalelo we-GRANT, osetyenziswa ukufaka iimvume zedata lomsebenzisi, kunye nomyalelo we-REVOKE, osetyenziswe ukususa iimvume ezikhoyo. Le miyalelo emibini yakha umgaqo-siseko wesondlo se-database.
Ulwakhiwo lwe-SQL Command
Ngethamsanqa kulabo abangenazo iinkqubo zekhompyutha, imiyalelo ye-SQL yenzelwe ukuba ne-syntax efana nesiNgesi. Ngokuqhelekileyo ziqala ngesitatimende somyalelo esichazela isenzo esithathayo, silandelwe isigatya esichaza ithagethi yomyalelo (njengetafile ethile ngaphakathi kwidata elichaphazelekayo ngumyalelo) kwaye ekugqibeleni, uluhlu lwamacandelwana anika imiyalelo eyongezelelweyo.
Ngokuqhelekileyo, ukufunda nje isitatimende se-SQL ngokuvakalayo kuya kukunika ingcamango enhle kakhulu yintoni umyalelo ekujoliswe ukuba ukwenze. Thatha isikhashana ufunde lo mzekelo wesitatimende se-SQL:
Unokuqiqa ukuba yintoni le nto izenzayo? Ifikelela kwitafile yomfundi wesiseko sedatha kwaye isusa zonke iirekhodi zabafundi abaphumelele ngo-2014.
UkuFunda iSQL Programming
Sijonge imizekelo embalwa ye-SQL elula kweli nqaku, kodwa i-SQL yilwimi ebanzi nolunamandla. Ukufumana isingeniso esicace ngakumbi, bona iSQL ezisemgangathweni .