Njengoba esabekwa SQL-ekuhlungeni?

Lapho ukusebenza yolwazi njalo kunesidingo baphethe umphumela nombuzo ngendlela ethile, isibonelo ngama-alfabethi. Ukuze wenze lokhu, le DBMS has a umsebenzi okhethekile e SQL - Ukuhlunga. Kulokhu, uMklami Ungakhetha ukuthi yiluphi amasimu lapho ukuze kuzoba ukufeza umphumela oyifunayo ngaphandle ukusetshenziswa amakhono sina izinhlelo.

Yini ihlelwa database?

Ukusebenza yolwazi ke njalo lixhumene yenqwaba ulwazi, okuyilona elidingekayo ukuthola ncamashí ukuhlelwa. Okwamanje, kunezinhlobo eziningi yolwazi, okuyinto has a ezahlukene izici, ethandwa kakhulu okuyizinto Oracle MS SQL. Imininingwane Uhlobo njengoba omunye izinqubo main database, enikezwe ekhethekile esakhelwe ngamunye wabo.

usezingeni idatha ukuba lula inqubo search, futhi kwezinye izimo, ukusiza ukuxazulula izinkinga noma nokwandisa ukusebenza kohlelo. SQL-uphenya ensimini eceleni ekhethiwe, futhi uma kudingekile, esimweni nezindinganiso ezifanayo nezinto mkhakha kungase kubonise amasethingi angeziwe, enquma indawo izintambo.

uhlobo umyalo

SQL-ukuhlunga in the database inikezwa ngokusebenzisa ORDER BY imisebenzi. Ngakho, i-bheke kolwazi kusukela database, ngemva ucacise amatafula namakholomu ukusuka lapho kuzokwenziwa ukufunda, isicelo kumele icacise umyalo uhlobo, bese unquma ukuthi uyafaneleka emkhakheni noma emikhakheni ukuthi uzobe ihlelwa.

Ngokwesibonelo, uma Abantu ithebula kudingeka uthole idatha kusuka Amasimu Igama Ubudala, ngesikhathi esifanayo ukubonisa imiphumela alfabhethi kwekholomu Igama, kuyokusiza ukuba wenze nombuzo ezilandelayo: KHETHA Igama, Ubudala KUSUKELA Abantu ORDER BY Igama.

Indlela ukusetha lokuhlunga?

izimo yamanje pose program ezihlukahlukene imisebenzi, futhi ngezinye izikhathi kuyadingeka ukuze anqume kusengaphambili ngokulandelana Imiphumela ziyobonakala - by wenyuka noma wehla oda, ngama-alfabethi noma oda reverse? Futhi ukuthi SQL uhlobo oda kunqunywa kwengezwa elisemqoka nombuzo. Ngemva kokukhetha le namasimu amatafula kuyiphi ulwazi olufunayo etholwe, kubalulekile ukwengeza ORDER BY ke ucacise igama kukholamu ofuna ukuhlunga.

Ukuze oda reverse kumelwe ucacise igama emva DESC ipharamitha. Uma izakhi ezimbili lula ezidingekile zindlela, bese amakholomu zihlukaniswe amakhoma, futhi simo kuqala uma emkhakheni enikezwa yokuthi kuza kuqala ohlwini. Kufanele kuqashelwe ukuthi ukuqondanisa izici in reverse ukuze ipharamitha DESC inikeza ensimini eyodwa kuphela, ngemva kwalokho igama okhiphé lesi elisemqoka, ngakho uma uludinga kuyadingeka ukuze ucacise wonke amakholomu akhethiwe.

Alternative izindlela ukuhlunga

Uma kungekho kungenzeka ngokusebenzisa esakhelwe SQL-ekuhlungeni, ungabhala omunye algorithm ezaziwayo. Uma kudingekile, ukuze sifinyelele esheshayo ukuhleleka kuka izakhi, kufanele asebenzise indlela "uhlobo okusheshayo", esekelwe afanayo isigamu-breaking. Futhi ifa elikhulu ukuthandwa rankings of "bubble" lapho izakhi ezimbili eduze emuva esimweni ilungiselelo ayilungile, "HeapSort" ithumela isici ngobukhulu e ekupheleni ohlwini, kanye "Ukufakwa uhlobo" kokuqagela indawo isici badedelane.

Nokho, ngokubhala ngesandla algorithm ngeke sivumele ukwandisa ijubane ukuhlunga uyothuthukisa ukuthuthukiswa kwamakhono izinhlelo, kodwa kuyokunika ukuguqula inqubo ngokulungisa uhlelo simo ngoba semininingwane ezithile ngcono uhlelo.