Ukubuyiswa kwedatha ngee-SQL Imibuzo: Ukwethulwa kweSitatimende se-SELECT

Ulwimi oluCwangcisiweyo lweeLwimi lunikeza abasebenzisi beenkcukacha-nkcukacha indlela yokubuyisela idatha enamandla kwaye eguqukayo. Kule nqaku, siza kujonga kwifom ngokubanzi yeSITETHO SOKUQALA kwaye ubhale imibuzo emfutshane yesampula yolwazi kunye. Ukuba le yindlela yakho yokuqala yokuqala kwiLizwe loLwimi oluCwangcisiweyo, unokufisa ukuphononongwa kwinqaku le-SQL Imfuneko ngaphambi kokuqhubeka.

Ukuba ukhangele ukwakhiwa kweenkcukacha ezitsha ukususela ekuqaleni, inqaku elithi Ukudala iiNgcaciso kunye neeTables kwi-SQL kufuneka zibonakalise i-point-off point point.

Kalokunje ukuba uququzelele kwizinto ezisiseko, makhe siqale ukuhlolisiswa kwesitatimende sokukhetha. Njengoko kunye nezifundo zangaphambili ze- SQL , siya kuqhubeka nokusebenzisa izitatimende ezihambelana nomgangatho we-ANSI SQL. Unokunqwenela ukubonisana namaxwebhu e-DBMS yakho ukuqinisekisa ukuba ngaba ixhasa iindlela eziphambili ezinokuphucula ukusebenza kunye / okanye ukusebenza kwekhowudi yakho ye-SQL.

Ifom yeGqwetha eliPhezulu

Ifom yefom ye-SELECT SELEKILE ibonakala ngezantsi:

Khetha i- list_list
NGOKUSUKA
LAPHO imeko (s)
IGQUBA ngokuthetha
UKUBA unesimo
BENZA ngegama

Umgca wokuqala wenkcazo utshela umprosesa we-SQL ukuba lo myalelo uyisitatimende sokukhetha kwaye sifuna ukufumana ulwazi oluvela kwisiseko sedatha. Uluhlu lwekhetho luvumela ukuba sikwazi ukuchaza uhlobo lolwazi esinqwenela ukulufumana.

Igatya elisuka kwi-ISIGABA esecaleni lesibini licacisa itheyibhile ethile (database) echaphazelekayo kwaye i- WHERE isigaba sinika ithuba lokunciphisa iziphumo kula maxwebhu adibana nemeko echaziweyo. Amagatya amathathu okugqibela afaka iimpawu eziphambili ngaphandle kweli nqaku - siza kuzihlola kwiimpawu zeSQL ezizayo.

Indlela elula yokufunda i-SQL ngumzekelo. Ngale nto engqondweni, makhe siqale ukukhangela imibuzo ethile. Kulo nqaku, siza kusebenzisa itafile yomqeshwa kwi-XYZ Corporation yolwazi lwesiseko yoluntu ukubonisa yonke imibuzo yethu. Nantsi itafile yonke:

Ukufumana iTheyibhile yonke

I-XYZ yoMlawuli weeNkonzo zoLuntu ufumana ingxelo yenyanga ehlinzeka ngemali kunye neengxelo zokunika ingxelo kumqeshwa ngamnye wenkampani. Isizukulwana sale ngxelo ngumzekelo wefom ye-SELECT yeyona ndlela elula. Ifunyanisa yonke into equlethwe kwitafile yedatha - nganye ikholomu kunye nomqolo. Nanku umbuzo oza kufeza esi siphumo:

UKUHLOLA *
KWABASEBENZI

Kulungile, kulungile? I-asterisk (*) ebonakala kwikhetho lokukhetha i-wildcard esetyenziselwa ukwazisa isiseko esinqwenela ukufumana ulwazi kuwo onke amakholomu kwitheyibhile yomqeshwa echazwe kwicandelwana elisuka kwi-FROM. Sifuna ukufumana yonke ingcaciso kwiziko ledatha, ngoko kwakungekho mfuneko ukusebenzisa isigatshana SEHLOKO ukukhawulela imigqa ekhethwe etafileni.

Nazi iziphumo zethu zeziphumo ezibonakala ngathi: