Ukubuyiswa kwedatha nge-SQL Imibuzo: Ukwethulwa kwesitatimende sokukhetha

Ulimi Olwenziwe Oluhlelekile lunikeza abasebenzisi bezinqolobane database indlela enamandla yokubuyisela idatha enamandla futhi eguquguqukayo - isitatimende sokukhetha. Kulesi sihloko, sizobheka ifomu elijwayelekile lesitatimende SOKUKHETHA bese ubhala imibuzo embalwa yesampula yolwazi ndawonye. Uma lokhu kuyi-foray yakho yokuqala emhlabeni weLimi OluHlangelwe Ulimi, ungase ufise ukubuyekeza izihloko ze-SQL ngaphambi kokuqhubeka.

Uma ubheka ukwakha i-database entsha kusukela ekuqaleni, isihloko esithi Ukudala Amadokhumenti namathebula ku-SQL kufanele kufakazele iphuzu elihle lokugxuma.

Manje njengoba usuqhekeze ezisekelo, ake siqale ukuhlola kwethu isitatimende SELECT. Njengemfundo yangaphambilini ye- SQL , sizoqhubeka ukusebenzisa izitatimende ezihambisana nesilinganiso se-ANSI SQL. Ungathanda ukubonisana namadokhumenti e-DBMS yakho ukuze unqume ukuthi isekela yini izinketho ezithuthukisiwe ezingahle zithuthukise ukusebenza kahle kanye / noma ukusebenza kwekhodi yakho ye-SQL.

I-General Form yeSitatimende SOKUKHETHA

Ifomu elijwayelekile lesitatimende sokukhetha livela ngezansi:

Khetha ukhetho lokukhetha
KUSUKA umthombo
LAPHO isimo (s)
I-GROUP BY expression
INGABE isimo
UKUBA ngegama

Umzila wokuqala wesitatimende utshela iphrosesa ye-SQL ukuthi lo myalo uyisitatimende sokukhetha nokuthi sifisa ukuthola ulwazi kusuka ku-database. Uhlu_ukukhetha luvumela ukuthi sikwazi ukucacisa uhlobo lwazi olufisa ukulithola .

Isigatshana esivela ku- FROM emgqeni wesibili sichaza ithebula (database) elithile elihilelekile elibandakanyekile futhi isigatshana se- WHERE sinikeza amandla okukhawulela imiphumela kulawo marekhodi ahlangabezane nemibandela ecacisiwe. Izigaba ezintathu zokugcina zimelela izici eziphambili ngaphandle kwalesi sihloko - sizozihlola ngezihloko ze-SQL ezizayo.

Indlela elula yokufunda i-SQL isibonelo. Ngalokho engqondweni, ake siqale ukubuka imibuzo ethile. Kulo lonke lesi sihloko, sizosebenzisa itafula lomsebenzi kusuka egciniwe le-XYZ Corporation yolwazi lwesintu ukuze sibonise yonke imibuzo yethu. Nasi ithebula lonke:

Ukubuyisa iThebula lonke

Umqondisi we-XYZ Corporation wezeMithombo Yabantu uthola umbiko wenyanga ohlinzeka ngolwazi lomholo kanye nokwazisa ngomsebenzi ngamunye wenkampani. Isizukulwane salombiko sibonelo sefomu lesitatimende se-SELECT esilula. Ilula nje yonke imininingwane equkethwe ngaphakathi kwetafula lemininingwane - zonke ikholomu kanye nomugqa ngamunye. Nansi umbuzo ozofeza lo mphumela:

Khetha *
KUSUKA abasebenzi

Kulungile kahle, kwesokudla? I-asterisk (*) evela ohlwini lokukhetha i-wildcard esetshenziselwa ukwazisa idatha esingathanda ukuyibuyisela ulwazi kuwo wonke amakholomu etafuleni lomsebenzi ekhonjisiwe kusigatshana esivela ku-FROM. Sifuna ukuthola lonke ulwazi ku-database, ngakho kwakungekho isidingo sokusebenzisa isigatshana se-WHERE ukukhawulela imigqa ekhethiwe etafuleni.

Nakhu ukuthi imiphumela yethu yombuzo ibonakala kanjani: