Kuchotsa Dongosolo ndi SQL Mafunso: Kuwunikira Phunziro la SELECT

Language Structured Query ikupereka ogwiritsa ntchito databata mphamvu zowonongeka zokhudzana ndi deta - ndondomeko ya SELECT. M'nkhaniyi, tiwone mawonekedwe onse a NKHANI ya SELECT ndikulemba zochepa zowonjezera zowonjezera mafunso pamodzi. Ngati ili ndilo loyamba lolowetsa mu dziko la Language Structure Query, mungafune kuti muwerenge mfundo za SQL Zopindulitsa musanapitirize.

Ngati mukuyang'ana kupanga kachidindo katsopano kuchokera pachiyambi, nkhani Yopanga Zithunzi ndi Matebulo mu SQL ziyenera kutsimikizira malo abwino ofulumira.

Tsopano kuti mwasuntha pazofunikira, tiyeni tiyambe kufufuza kwa ndondomeko ya SELECT. Mofanana ndi maphunziro a SQL apitawo, tipitiliza kugwiritsa ntchito mawu ogwirizana ndi ANSI SQL. Mungafune kuwona zolemba za DBMS yanu kuti mudziwe ngati zikuthandizira zosankha zomwe zingapangitse kuti SQL yanu ikhale yoyenera komanso / kapena yogwira ntchito.

Fomu Yowonjezera ya Chisankho cha SELECT

Maonekedwe onse a mawu a SELECT akuwoneka pansipa:

SANKANI kusankha mndandanda
Kuchokera ku gwero
PAMENE vuto (s)
GROUP BY mawu
KODI muli ndi vuto
YAM'MBUYO YOTSATIRA

Mzere woyamba wa mawuwo umauza S processor SQL kuti lamulo ili ndi ndondomeko ya SELECT ndi kuti tikufuna kulandira chidziwitso kuchokera ku database. Chosankha_chilisankha chimatilola kufotokoza mtundu wa chidziwitso chomwe tikufuna kuchipeza.

Chigamulo cha FROM kuchokera mu mzere wachiwiri chimatanthauzira tebulo lachinsinsi lomwe likukhudzidwa ndi WHERE ndime imene imatipatsa mphamvu yothetsera zotsatira kwa omwe akulemba zomwe zikugwirizana ndi zikhalidwezo . Zigamulo zitatu zomalizira zikuyimira zida zapadera zomwe sizinachitike pa nkhaniyi - tidzazifufuza m'ma SQL nkhani zam'tsogolo.

Njira yosavuta yophunzirira SQL ndi chitsanzo. Ndili ndi malingaliro, tiyeni tiyambe kuyang'ana mafunso ena. M'nkhani yonseyi, tigwiritsa ntchito tebulo la wogwira ntchito kuchokera ku chinsinsi cha XYZ Corporation cha anthu kuti tiwonetse mafunso athu onse. Pano pali tebulo lonse:

Kuchotsa Pulogalamu Yonse

XYZ Corporation wa Director of Human Resources amalandira lipoti la mwezi uliwonse kupereka malipoti ndi malipoti kwa wogwira ntchito aliyense. Mbadwo wa lipoti ili ndi chitsanzo cha mawonekedwe osavuta a mawu a SELECT. Icho chimangopeza zonse zomwe ziri mu tebulo lachinsinsi - gawo lililonse ndi mzere uliwonse. Pano pali funso lomwe lidzakwaniritsa zotsatira izi:

CHISANKHO *
KUchokera kwa antchito

Ndendende molunjika, molondola? Thesterisk (*) ikuwonekera pazondandanda_dongosolo lakale lomwe likugwiritsidwa ntchito kudziwitsa deta yomwe tikufuna kuti tipeze mauthenga kuchokera kuzitsulo zonse mu tebulo la ogwira ntchito lomwe likupezeka mu CHIYAMBI CHOKUKHALA . Tinkafuna kuti tipeze zonse zomwe zili m'masitomu, choncho sizinali zofunikira kugwiritsa ntchito ndime YOYAMBA kuti ikhale yoletsa mizere yosankhidwa kuchokera patebulo.

Nazi zomwe zotsatira zathu zokhudzana zikuwoneka ngati: