Chii chinoita SQL CONCAT chaitika?

Kushanda Databases kunoramba chokuita kuwana mubvunzo zvabuda. Uye mune zvimwe zviitiko, mashoko aya anofanira kuiswa chinovhara imwe nzira kana chokubatanidza nevamwe mashoko. Kugadzirisa dambudziko iri pane SQL basa - CONCAT.

Chii chinoita CONCAT ishande?

Kana kuita zvimwe basa pamwe Databases, pane kudiwa pachiimbwa mamwe mashoko mitsetse kana pakati pachavo. Kugadzirisa dambudziko iri pane SQL basa - CONCAT. Kana kurishandisa maviri kana kupfuura mitsetse zvichabviswa akabatanidza kupinda chimwe. In ichi concatenation oparesheni zvakarurama akaita se vari tambo, uye kusanganiswa variables.

Mune dzimwe Databases, SQL CONCAT ane mhando dzakawanda. Somuenzaniso, muna MySQL ine ishamwari kwayo - CONCAT_WS. Kusiyana mabasa hakukoshi: panyaya wokutanga, kana pamwe chete nharo ane mutengo uri null, mugumisiro wacho concatenation riri null, uye kushandisa wechipiri musimboti kubatanidza razero operand iri nyore akapembera.

shanda nemarongerwo

Kana tichishandisa CONCAT basa, SQL-nemarongerwo rinoda programmer kushandisa pfungwa iri kuti umo operands zvinofanira akabatanidzwa. Sam tambo concatenation akavhiyiwa nemarongerwo iri kumbonyanya nyore: mushure CONCAT guru iri mumabhuraketi, akaparadzaniswa nevanhu nezvitura befu anoratidza ose anodiwa nharo kana mitsara kuitira, uye pashure yokupedzisira parenthesis, kana zvakakodzera, anoratidza AS guru uye zita shanduka iyo mugumisiro zvichabviswa kunyorwa. CONCAT basa template sezvinotevera:

CONCAT (string1, string2 [, mutsetse 3, ...]) [AS var_name].

Zvinofanira kucherechedzwa kuti sezvo mibvunzo mashandiro anogona kushandiswa operand uye tambo kusanganiswa tsika, uye mashandiro unodzokera somugumisiro. Somuenzaniso, SQL CONCAT oparesheni pacharo. Saka, nokushanda nheyo nested zvitsigiso.

Maitirwo pasina kushandisa CONCAT?

Kana kunodiwa kudiwa kuita pasina kushandisa kuvhiyiwa, kana programmer hazvizivikanwi CONCAT basa, kuti SQL anopa mumwe mamwe musiyano pakati tambo concatenation. Kuti aite izvi, shandisa "+" opareta, asi izvi ine nhamba zvinhu zvinofanira kufungwa kana tichishanda naye.

Kana kushandisa "+" kana operands vari kusanganiswa tsika, nokushanda mugumisiro uchava zvake kuwedzera nhamba, uye nokubatanidza nerwonzi nhamba pasina kutendeuka chirongwa yakajeka achadzoka chikanganiso kana zvakakodzera. Saka, kana inotevera mubvunzo mugumisiro ndiko kukosha "6":

Sarudza 1 + 2 + 3.

Zvikasadaro vose dzinoshandiswa akafanana uye kudzokera chete mugumisiro.