Coalesce sql: kufotokoza, kugwiritsa ntchito, zitsanzo

Mukamapanga ma sql-queries, nthawi zambiri zimachitika kuti mukasankha deta, muyenera kuyerekeza miyeso ya zipilala zingapo ndipo mutulutsa chimodzi mwa izo zomwe zili ndi deta (osati chopanda kanthu). Vutoli limathetsedwa bwino ndi mawu akuti Coalesce. M'nkhaniyi mupeza tsatanetsatane wa mawu akuti Coalesce sql, kufotokozera zochitika za ntchito, komanso zitsanzo.

Kupezeka kwa mfundo zosagwirizana ndi Coalesce. Zida

Taganizirani za Sql Coalesce zomwe zimagwiritsidwa ntchito:

1. Zimapereka kufotokozera zifukwa zilizonse (kusiyana ndi Isnull / Nvl / Nvl2, chiwerengero cha zifukwa zomwe zili zochepa).
2. Angavomereze ma subqueries ngati mkangano.
3. Ibwetsanso zotsatirazo zofanana ndi mtengo woyamba wosakhala wa Null, kapena Null, ngati palibe phindu likupezeka.
4. Sql Coalesce angagwiritsidwe ntchito mu Chingerezi kusankha kusankha chinthu chopanda kanthu, komanso Kumene munganene kuti ndondomeko ya zikhomo zopanda kanthu sizingaloledwe (/ kuloledwa).
5. Mawu awa ndi ofanana ndi kugwiritsa ntchito mafotokozedwe a Mlanduwu, kufufuza ndemanga iliyonse motsatira mkhalidwewu Pamene mkangano1 ulibe kanthu kenakake1. Ndipotu, Coalesce ndi "njira yochepetsera" yokonzedweratu kugwiritsiridwa ntchito, ndipo m'mabuku ambiri a DBMS funso lothandizira lilembanso mawu a Coalesce pa Nkhani.
6. Zomwe Sql Coalesce ali nazo zilipo muzinthu zonse zoyendetsera machitidwe ogulitsa ma database.

Syntax Coalesce

Aliyense amene wagwiritsira ntchito Coalesce kuti asonkhanitse mafunso a sql amadziwa kuti mawu a mawuwa ndi osavuta. Zokwanira kufotokozera pazifukwa zotsatizana zomwe zimayang'aniridwa pa Null, zosiyana ndi makasitomala. Ngati tiganiza kuti zifukwazo zili ndi mayina arg1, arg2, ... argN, ndiye Coalesce syntax idzawoneka ngati iyi:

Coalesce (arg1, arg2, ... argN).

Tidzakonzekera matebulo angapo kuti tiphunzire njira ya mawu awa.

Kukonzekera matebulo

Kuti timvetse bwino mafotokozedwe a Coalesce sql, tidzakhazikitsa magome awiri omwe ali ndi zidziwitso pa zinthu zogulitsa katundu.

Malo oyamba a tebulo ayenera kukhala ndi mayina a zinthu zogulitsa nyumba ndi dera lawo. Dera likhoza kufotokozedwa (area_yt) kapena kulengeza (area_decl).

Tebulo lachiwiri la Basic_characteristic liyenera kukhala ndi chidziwitso pa chikhalidwe chachikulu cha chinthu cha nyumba yogulitsa katundu - Kuwonjezera, Kuzama, Chigawo, Kukula, Kutalika.

Tinafufuza chiganizo cha Coalesce sql, kufotokozera, zizindikiro za ntchito, ndikupitiliza zitsanzo.

Zitsanzo za ntchito

Chidule cha mawu a Coalesce ndi chophweka kwambiri, koma ndibwino kukumbukira kuti zotsatira za lamulo lidzakhala chinthu choyamba chopanda kanthu chomwe chimapezeka kuchokera mndandanda wamakangano. Ndemanga iyi ndi yofunika kwambiri, choncho zotsutsana m'mawuwo ziyenera kukhazikitsidwa kuti zikhale zofunika. Njira yosavuta kumvetsetsa mfundo ya m'deralo. Pangani pempho limene limasankha dzina la malo, komanso malo omwe akufunika:

Ndipo zotsatira zake:

Kwa zinthu "Kumanga 1", "Land plot 1" ndi "Construction 2", maiko onse awiriwa adadzazidwa, koma pa malo oyamba anali malo oyeretsedwa, popeza tawalemba pa mndandanda wa zifukwa zoyamba. Mawu akuti Coalesce adapeza chinthu choyamba chopanda chopanda kanthu ndipo adachichotsa, kuleka kuyang'ana kwina kwa mfundozo. Kukonzekera kwa pempholi kuli kolondola, chifukwa dera lomwe likulankhulidwa ndilochindunji kuposa lomwe linaloledwa. Ngati tilongosola malo omwe adatchulidwa ngati mtsutso woyamba, ndiye ngati gawo ili ladzaza liri lonse, lidzakhala loyambirira.

Kuwonjezera pa kugwiritsa ntchito mu Kusankha, kawirikawiri mawu a Coalesce amagwiritsidwa ntchito ndi Gawo Lomwe. Amakulolani kuti muchotse zotsatira zomwe mndandanda wa masamba ulibe (kapena mosemphana ndi zina, ziphatikizapo mfundo zomwezo pazomwe mulibe mndandanda wa masamba). Izi zili paliponse: mwachitsanzo, panthawi yolembera wogwira ntchito watsopano, zowonjezereka zokhudzana ndi wogwira ntchitoyo zidalowa mu databata, ndipo mfundo zatsatanetsatane zinasiyidwa "kwa mtsogolo". Pang'onopang'ono, "ziphuphu" zikuyendayenda - kaya isanafike chitsimikizo, kapena pamene mutumiza wogwira ntchito paulendo / bizinesi ulendo / odwala odwala.

Sankhani kuchokera pa tebulo ndi zikuluzikulu za zinthu zogulitsa nyumba, zomwe sizidzaza ndi makhalidwe omwe ali nawo:

Kwa funso ili, pali mzere umodzi mu tebulo - chinthu "Land plot 1", momwe malo onse okhala ndi makhalidwe ali opanda kanthu:

Tikukhulupirira kuti ndondomeko yathu yowonjezera Coalesce sql inakuthandizani kumvetsetsa zonse zomwe mukugwiritsa ntchito mawuwa, komanso kuthana ndi maonekedwe ofunikira.