He aha hanga SQL CONCAT mahi?

Mahi ki ngā pātengi raraunga ko te tonu e pā ana ki te whiwhi hua rapu. A i roto i ētahi wā, kia kawea mai tenei kōrero ki te mata i roto i te ara etahi ranei ki ngā ki ētahi atu raraunga. Hei whakaoti i tēnei raruraru i reira ko te mahi SQL - CONCAT.

He aha hanga te mahi CONCAT?

A, no te raveraa i etahi mahi ki pātengi raraunga, i reira he he hiahia i roto i te taha ki te raina raraunga atu ranei i waenganui ia ratou. Hei whakaoti i tēnei raruraru i reira ko te mahi SQL - CONCAT. Ka A, no te whakamahi i te reira e rua, neke atu rānei ngā rārangi e hanumi ki tetahi. I roto i tenei mahi concatenation te tika whakamana rite i roto i te aho, me ki taurangi tau.

I roto i te tahi mau pātengi raraunga, He maha ngā momo SQL CONCAT. Hei tauira, i roto i MySQL kua reira tona tauira - CONCAT_WS. Ko te rerekētanga i waenganui i te mahi iti: i roto i te take o te tuatahi, ka ngā ki te tautohe nei uara ko korengia, te hua o te concatenation he korengia, me te whakamahi i te rua o nga whakatinanatanga whakakotahi te tauwhakaarotau kore te pekepeke noa.

mahi wetereo

A, no te whakamahi i te mahi CONCAT, titau SQL-wetereo te kaihātepe ki te whakamahi i te tautohetohe i roto i te raupapa i roto i nei te tauwhakaarotau e ki kia piri. Ko te tino ohie Sam ngā mahi string concatenation wetereo: i muri i te kupu matua CONCAT i roto i taiapa, wehea e ngā piko tohu nga tautohetohe tika katoa rarangi ranei i roto i te tikanga, me muri i te reu kati, ki te tika, tohu te kupu matua AS me te ingoa o te tāupe i roto i nei e te hua e tuhia. CONCAT tātauira mahi e whai ake:

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

Me kï reira e rite taea te whakamahi i te tohenga o te mahi kia rite ki te tauwhakaarotau me te string o uara ā-tau, me te mahi e hoki te hua. Hei tauira, mahi SQL CONCAT iho. Ko te kupu, ko te parau tumu mahi o te tautoko ohanga e.

Me pēhea te ki te mahi i waho o te whakamahi CONCAT?

I roto i te take i reira i reira he he hiahia ki te mahi i waho o te whakamahi o te pokanga, te kaihātepe he unknown mahi CONCAT ranei, te SQL tuku tetahi atu kē o aho concatenation. Ki te mahi i tenei, te whakamahi i te "+" operator, engari he maha o ngā āhuatanga e hiahia ana ki te kia whakaaro ina mahi ki a ia i tenei huarahi kua.

A, no te whakamahi i "+" ki te ko te tauwhakaarotau uara tau, te hua mahi ka waiho hei tua noa o tau, a ngā ki te tau aho, kahore hōtaka faafariuraa mārama ka hoki te hapa, ki te tika. Ko te kupu, ka te hua rapu muri ko te uara o "6":

WHIRIWHIRI I 1 + 2 + 3.

Kore e ōrite tikanga e rua me te hoki i te hua taua.