Ana dawo da bayanai tare da tambayoyi SQL: Gabatar da Bayanan SELECT

Harshen Sakamakon Lissafi yana ba masu amfani da labaran kayan aiki mai mahimmanci da sauƙi mai mahimmancin bayanai - bayanin sanarwa. A cikin wannan labarin, zamu duba kundin tsarin bayanin SELECT da kuma rubuta wasu tambayoyin tambayoyin bayanai tare. Idan wannan ne karo na farko da kuka shiga cikin duniya na Harshen Sakamakon Structured, ƙila kuna so su sake nazarin labarin SQL Asusun kafin ci gaba.

Idan kana neman zayyana sabon labarun daga farfado, labarin da ke samar da Databases da Tables a cikin SQL ya kamata ya tabbatar da kyakkyawar matsala.

Yanzu da ka yi fice a kan kayan yaudara, bari mu fara nazarin bayanin sanarwa. Kamar yadda koyarwar darussan baya na baya, za mu ci gaba da amfani da maganganun da suka dace tare da daidaitattun ANSI SQL. Kuna iya tuntuɓar takardun don DBMS don ƙayyade ko yana goyan bayan zaɓuɓɓukan ci gaba waɗanda za su iya inganta haɓaka da / ko inganci na lambar SQL ɗinku.

Gaba ɗaya na Bayanan SELECT

Nau'in sashin bayanin SELECT ya bayyana a kasa:

Sake zabe_list
FROM source
YADDA yanayin (s)
Ƙungiyar ta magana
KASA yanayin
GARANTI DA magana

Lissafin farko na sanarwa ya shaida wa mai sarrafa SQL cewa wannan umarni ne bayanin sirri na SELECT kuma muna so mu dawo da bayanin daga wani asusun. Zaɓin zaɓi ya ba mu damar saka irin bayanin da muke son kawowa.

Sashe na DAGA a cikin layi na biyu ya ƙayyade ɗakin tabbacin da aka ƙunsa da kuma WANNAN SABARI yana ba mu damar da za a ƙayyade sakamakon zuwa waɗannan bayanan da suka dace da yanayin da aka ƙayyade. Ƙarshe na uku na uku suna nuna siffofin ci gaba a waje da wannan labarin - zamu bincika su a cikin abubuwan SQL a gaba.

Hanyar mafi sauki don koyi SQL shine ta misali. Tare da wannan a zuciyarsa, bari mu fara kallon wasu tambayoyin tambayoyi. A cikin wannan labarin, za mu yi amfani da teburin ma'aikaci daga fannin fasaha na kamfanin XYZ Corporation don tabbatar da dukan tambayoyinmu. Ga dukan tebur:

Sake dawo da Dukkan Lafi

Ma'aikatar Harkokin Kasuwancin ta XYZ ta samu rahoton kowane wata na bayar da albashi da bayar da rahoto ga kowane ma'aikacin kamfanin. Rahoton wannan rahoton shine misali na bayanin sanarwa mafi sauki. Yana kawai ya dawo da dukkanin bayanan da ke ciki a cikin wani tashar bayanai - kowane shafi da kowane jere. Ga wannan tambaya da za ta cim ma sakamakon wannan:

SANTA *
FROM ma'aikata

M kyauta mai sauƙi, dama? Alama (*) wanda yake fitowa a cikin select_list ne mai amfani da aka yi amfani dashi don sanar da asusun da za mu so a dawo da bayanan daga dukkanin ginshiƙai a cikin teburin ma'aikacin da aka gano a cikin sashe FROM FROM. Muna so mu dawo da dukkanin bayanan a cikin database, saboda haka ba lallai ba ne a yi amfani da wata maƙasudin wuri don ƙuntata layuka da aka zaɓa daga tebur.

Ga abin da sakamakon binciken mu ya yi kamar: