Kubwezeretsa Data Kuchokera Mapepala Ambiri Ndi SQL Yowonjezera Kwawo

Wowonjezera akuphatikizanso uthenga wobwereza womwe umapezeka muzithunzi ziwiri kapena zambiri

Maubwenzi amkati ndi omwe amagwiritsidwa ntchito mobwerezabwereza mu SQL. Iwo amabwereranso zokhazokha zomwe zilipo m'ma tebulo awiri kapena kuposa. Mgwirizanowu umatsimikizira kuti ndizolemba ziti zomwe zimagwirizanitsidwa palimodzi ndipo zimatchulidwa mu GAWO LIMENE. Mwachitsanzo, ngati mukufuna mndandanda wa maulendo oyendetsa galimoto / galimoto yomwe magalimoto onse ndi dalaivala ali mumzinda womwewo, funso ili la SQL lotsatira likugwira ntchitoyi:

SELECT lastname, firstname, tag KUYENDA madalaivala, magalimoto PAMENE madalaivala.location = magalimoto.malo

Nazi zotsatira:

dzina lanu loyamba
----------- ------------ ----
Baker Roland H122JM
Smythe Michael D824HA
Smythe Michael P091YF
Jacobs Abraham J291QR
Jacobs Abraham L990MT

Tawonani kuti zotsatira ndizo zomwe zinafunidwa. N'zotheka kupititsa patsogolo funsoli pofotokozera zina zowonjezera mu GAWO LIMENE. Ganizirani kuti zoyambirirazo zikuyenderana ndi oyendetsa magalimoto omwe saloledwa kuyendetsa galimoto (madalaivala amoto kupita ku magalimoto komanso mosiyana). Mungagwiritse ntchito funso lotsatira kuthetsa vuto ili:

SELECT lastname, firstname, tag, cars.class KUYENDA madalaivala, magalimoto PAMENE madalaivala.location = magalimoto.kuyika ndi madalaivala.class = magalimoto.class

Chitsanzo ichi chikulongosola tebulo loyambira pa chigawo cha m'kalasi mu SELECTION SECTION chifukwa kalasiyo ndi yosavuta-iyo ikuwoneka pa matebulo awiriwo. Makhalidwe nthawi zambiri amatha kufotokozera ndondomeko ya tebulo yomwe iyenera kuphatikizidwa mu zotsatira zotsatira. Pankhani iyi, sizimapanga kusiyana, monga zigawo zili zofanana ndipo zimagwirizanitsa ntchito equijoin. Komabe, ngati zigawozo zili ndi deta yosiyana, kusiyana kumeneku kungakhale kovuta. Nazi zotsatira za funso ili:

dzina loyamba lachitsulo
---------- ------------ --------
Baker Roland H122JM Galimoto
Smythe Michael D824HA Ngolo
Jacobs Abraham J291QR Galimoto

Mizere yosasoweka Michael Smythe anaika pa galimoto ndi Abraham Jacobs kupita ku galimoto, magalimoto omwe sanaloledwe kuyendetsa galimoto.

Mukhozanso kugwiritsanso ntchito mkati mwa kuphatikizapo data kuchokera pa matebulo atatu kapena angapo .