Okwenza SQL CONCAT umsebenzi?

Ukusebenza yolwazi njalo elihlobene ne ukuthola nombuzo imiphumela. Kanti kwezinye izimo, lolu lwazi kufanele alethwe esikrinini ngendlela ethile noma ukuhlanganisa nenye idatha. Ukuze uxazulule le nkinga kukhona umsebenzi SQL - CONCAT.

Yini eyenza umsebenzi CONCAT?

Uma wenza umsebenzi othile nge yolwazi, kunesidingo ngokuhlanganyela ezengeziwe idatha imigqa noma phakathi kwabo. Ukuze uxazulule le nkinga kukhona umsebenzi SQL - CONCAT. Lapho uyisebenzisa imigqa emibili noma ngaphezulu kuzohlanganiswa zibe munye. Kulesi msebenzi concatenation kahle kwenziwe njengoba e-string, futhi eziguquguqukayo zezinombolo.

Kwezinye yolwazi, SQL CONCAT has izinhlobo eziningana. Ngokwesibonelo, ngo-MySQL it has sabafowabo - CONCAT_WS. Umehluko emkhatsini imisebenzi engabalulekile: endabeni yokuqala, lapho kuhlangene i-agumenti ogama value kuyinto null, umphumela we-concatenation kuyinto null, futhi usebenzisa samuntu yesibili ngokuhlanganisa zero we- omane yeqiwe.

umsebenzi-syntax

Lapho usebenzisa umsebenzi CONCAT, SQL--syntax kudinga uhlelo ukusebenzisa agumenti ngokulandelana lapho operands kumele bajoyine. Sam string concatenation imisebenzi kwemavi kahle elula: emva elisemqoka CONCAT kubakaki, kuhlukaniswe ukhefane ukubonisa wonke ama-agumenti noma imigqa ezidingekayo ukuze, futhi ngemva abakaki lokuvala, uma kunesidingo, ukhombise NJENGOBA elisemqoka futhi igama okuguquguqukayo okuyinto umphumela kuzoqoshwa. CONCAT umsebenzi isifanekiso kanje:

CONCAT (iyunithi yezinhlamvu1, iyunithi yezinhlamvu2 [, umugqa 3, ...]) [AS var_name].

Kufanele kuqashelwe ukuthi njengoba emaphuzwini umsebenzi ingasetshenziswa njengomsebenzi we- futhi intambo ye amanani ezinombolo, kanye umsebenzi ibuyisa yi. Ngokwesibonelo, SQL CONCAT ukusebenza ngokwalo. Ngakho, isimiso ekusebenzeni izisekelo izidleke.

Kanjani ukwenza ngaphandle CONCAT ukusetshenziswa?

Esimweni lapho kukhona isidingo sokwenza ngaphandle kokusebenzisa ukuhlinzwa, noma uhlelo ayaziwa CONCAT umsebenzi, SQL inikeza eyodwa ngaphezulu okufana string concatenation. Ukuze wenze lokhu, sebenzisa "+" opharetha, kodwa le ndlela has eziningi izici ezidinga kubhekwe uma usebenza naye.

Uma usebenzisa "+" uma operands kukhona amanani ezinombolo, umphumela ukusebenza kuyoba yinto kwalokho abavamile izinombolo, okuhlangana ngayo izinombolo umugqa ngaphandle Uhlelo okubeka obala ukuguqulwa uzobuya nephutha uma kunesidingo. Ngakho, lapho nombuzo yi esilandelayo ukubaluleka "6":

KHETHA 1 + 2 + 3.

Kungenjalo kokubili izindlela ayafana bese ubuyela umphumela ofanayo.