Select mawu (SQL)

Choka SQL chidule yokha (chinenero zosanjidwa mafunso) akuganizira chakuti pamafunika - amafotokozera kaŵirikaŵiri ntchito SQL. Sankhani mizere ya, basi kuthetsa deta kuthetsa, kuvina kapena reorder mizati kuthandiza Select (SQL) - mawu munali limasonyeza Nawonso achichepere kubweretsa zinthu zina.

malembedwe

Bwino ntchito woyendetsa aliyense ayenera choyamba mutidziwe ndi malembedwe a chinenero mapulogalamu pansi kulingalira. Pokambirana makamaka za chinenero SQL, Select (woyendetsa) ali malembedwe zotsatirazi:

Sankhani	Limafotokoza Nawonso achichepere kuti titadutsa pa pempho. nfundo yaikhulu izi.
Chimodzi, ziwiri, zitatu ...	Lembani kusonyeza mizati
kuchokera	Umasonyeza dzina la tebulo limene deta adzakhala anasankha. Ndi kuvomerezedwa nfundo yaikhulu.

Izi otchedwa "lalifupi" woyendetsa malembedwe, koma umatiuza ife chakuti popanda mawu Select ndi ku Nawonso achichepere si kutsatira pempho lathu.

Full mawu malembedwe zikusonyezedwa chithunzi zotsatirazi:

Apa Kodi mzera amalola kuti sule pofufuza kutchula zinthu.

Pakuti mfundo za grouping ndi ntchito nawo za akaphatikiza ntchito ntchito kupereka Gulu, ndi kulongosola bwino chifukwa pambuyo grouping amagwiritsa Kukhala mukuiganizira.

Order mtundu zidzathandiza mfundo za ndime anasankha kukwera kapena kutsika dongosolo.

с информацией: Kuona kuti ndi Select mawu, amaganiza kuti Nawonso achichepere athu ali zotsatirazi tebulo Amphaka mderali:

ID	zimaswana	dzina	Birthday	mtundu
1	Bobtail	mbuye	04/01/2017	Gray
2	pindilani	feint	03/16/2017	White
3	Mau	Panther	03/30/2017	Black
4	Bobtail	Tyson	02/23/2017	Gray
5	Burmilla	Athena	08/01/2017	Black

Mzera uliwonse uli wapadera chipinda Kitty, mtundu wake, dzina, tsiku lobadwa ndi mitundu. Tionanso mmene woyendetsa Select (SQL), kale zochokera kafukufuku tebulo.

Monga deta ndi mumtengo pagome

Monga kudafotokozedwa pamwamba, kuti chikhale chitsanzo cha mfundo muyenera pagome ife ntchito mawu.

Nfundo yaikhulu n'chakuti Select mizati kusonyeza. Mukhoza kupanga mndandanda wa mizati chofunika, ankasiyana mipatuliro, ndiye dongosolo lonse lidzaonekera izi:

Sankhani mtundu, mtundu, dzina kuyambira Amphaka

Monga mukuonera, titha kukonza mizati mu ndondomeko imene ali m'mavuto. Komanso, ife tikuona yekha makoma zofunika kwa ife.

Palinso shorthand kwa mizati onse view tebulo. Kuti tichite zimenezi, pambuyo Select amasonyeza kuti asterisk (*) ndi danga. Dongosolo lonse lidzaonekera izi:

Sankhani * kuyambira Amphaka

The chifukwa cha kafufuzidwe pamwamba - lonse Amphaka tebulo, kuwonetsa mawonekedwe umene uli kumapeto kwa gawo lapitali.

Anthu ambiri amadabwa mmene malo a ntchito mu SQL Select mu mzere. Nthawi zambiri izi chofunika pamene mukufuna kuphatikiza dzina la dzina ndi patronymic munthu anaikidwa mizati kulekanitsidwa.

Pankhaniyi, ife kuphatikiza Mitundu ndi mitundu ya amphaka Amphaka tebulo. Nuance ndi zinasokoneza makompyuta osiyana ntchito chingwe concatenation a zilembo zosiyanasiyana. Nthawi zina izo zangokhala kuphatikiza (+), mu zina - wachiphamaso mzere Mbali (||) kapena ampersand (&), nthawi zina amagwiritsidwa ntchito ndi operand Concat. Choncho, asanayambe kaphatikizidwe kufunika kuwerenga Zamkati kuti Nawonso achichepere zenizeni zimene mukuchita.

Sankhani mtundu || ',' || mtundu kuyambira amphaka

Chifukwa ife tikufika zotsatirazi:

Zimaswana, Mtundu

Bobtail, Gray

Pindilani, White

Mau, Black

Bobtail, Gray

Burmilla, Black

Kucotsa deta kuthetsa

Osiyana - Ntchito Select (SQL), imene imathandiza kupewa mwendo zingwe mwamtheradi zofanana zotsatira chitsanzo.

Mwachitsanzo, tikufuna kudziwa zimene mphaka Mitundu ndi tebulo wathu. Ngati mumamwa ndi kafufuzidwe losavuta:

Sankhani mtundu kuyambira Amphaka

Ndiye ife kupeza chifukwa ankayembekezera:

zimaswana

Bobtail

pindilani

Mau

Bobtail

Burmilla

Monga mukuonera, Bobtail zimasokoneza ndi lingafanane kawiri. Mtsutso osiyana kupewa mwendo, tiyenera okha kuwonjezera funso ili:

Sankhani mtundu osiyana kuyambira Amphaka

pempho powunikira

Mu zenizeni, pafupifupi pempho palibe sakutero linanena bungwe deta monga lonse la mizere tebulo. Taonani maganizo a Select (SQL) adzalola kuthandauza akugwirizana ndi kusankha chabe mizere lamanja.

Choncho chuma ichi Kodi. pempholo likukhudza mkhalidwe - mawu pokhapo titachitapo amene amapereka phindu linanena bungwe ndi "oona" kapena "wabodza." Select mawu adzakhala wachotsa yekha deta pagome zimene mawu makonzedwe anayenera N'zoona kapena "choonadi".

Zimathandiza kuthana ndi kumanga izi, chitsanzo yosavuta. Tiyerekeze tikufuna kudziwa zonse za amphaka a mtundu wakuda.

Sankhani * kuyambira amphaka Kodi mtundu = 'Black'

The chifukwa cha kafufuzidwe uyu adzakhala mzere lotsatira pa tebulo:

3	Mau	Panther	03/30/2017	Black
5	Burmilla	Athena	08/01/2017	Black

Mukhozanso kuphatikiza zinthu pogwiritsa ntchito zizindikiro zosinthira zomveka Ndipo, Kapena, Osati.

Kupereka Gulu mwa

Kupereka Gulu mwa ntchito Select (SQL), zimathandiza gulu kafufuzidwe ndi phindu la ndime yeniyeni (kapena mizati), kenako kuwatsatira kugwira ntchito ndi akaphatikiza.

Pakuti ntchito akaphatikiza monga:

• Werengerani - linaŵerengera chiwerengero cha mizere osankhidwa ndi funso.
• Uwerenge - pa masamu Uwerenge onse ndime anasankha.
• Min - zotuluka osachepera ndime anasankha.
• Max - motero, pazipita mfundo za ndime anasankha.
• Avg - kufunika pafupifupi.

Chiwembu cha pempholo bwino mwacitsanzo. Tiyerekeze tikufuna kupeza momwe mlingo wa amphaka mtundu tili. Kuti tichite zimenezi, kulenga zotsatirazi kafufuzidwe losavuta:

Sankhani mtundu, kuwerengedwa (*) kuyambira amphaka Gulu mwa mtundu

The chifukwa cha chifuniro mu tebulo zotsatirazi:

zimaswana	Werengerani
Bobtail	2
pindilani	1
Mau	1
Burmilla	1

Monga mukuonera, bobtail amphaka kawetedwe tili awiri, ena monga limodzi. Pa pempho la Chizolowezi, zochokera tebulo wathu, mahatchiwo amatha kumvetsa zimene amphaka Mitundu ndi mu ankafuna pakati makasitomala, ndi chomwe - palibe.

Zikuoneka kuti chifukwa cha nambala yaikulu zolemba mu tebulo leni amafunabe kulongosolerana pempho ndi kusonyeza okha amphaka amenewa, omwe anali osaposa Mwachitsanzo, khumi. Kulongosolerana kapena magulu fyuluta ntchito Kukhala mukuiganizira. Kumatithandiza kuti achotse magulu ena, ofanana Kodi mzera, amene amatayira mizere ena. chikhalidwe ndi chimafotokozera kugwira ntchito akaphatikiza. Lembani pempho:

Sankhani mtundu, kuwerengedwa (*) kuyambira amphaka Gulu mwa mtundu Kukhala kuwerengedwa (*) <= 10

Popeza chikhalidwe tinapemphedwa "chiwerengero cha amphaka aliyense mtundu si oposa 10", chifukwa ife tikufika ndi chimodzimodzi mu chitsanzo, popanda kutchula. Koma apa ndikofunika kumvetsetsa chiwembu yokha ntchito Kukhala mukuiganizira. Koma ngati inu kusintha chikhalidwe mfundo pa Kukhala kuwerengedwa (*) = 1, ndiye zotsatira adzakhala kusanduka mizere itatu ndipo amasonyeza amphaka, zimenezi zinachititsa imodzi yokha.

kusanja

Dziŵani ndi Order mwa - kupereka Select (SQL) woyendetsa kuti amalola kuthetsa mizere linanena bungwe mu kukwera kapena kutsika kuti madanga umodzi kapena kuposerapo.

Nkofunika kukumbukira kuti Order ndi - ndi kupereka chomaliza onse Select mawu dongosolo. Izo aikidwa pambuyo Select, Kuchokera, kuti Gulu mwa, Okhala.

Pali mfundo zitatu zofunika pa kusanja:

1) Mukhoza kukhazikitsa chiwerengero cha mizati, omwe aliyense payekha akhoza zosankhidwa kaya akukwera (ASC), kapena kutsika (DESC).

2) makoma onse pamwamba pa Order ndi chiganizo akhale m'gulu makoma anasankha Select.

3) unsankhula mndandanda mayina enieni kuthetsa mizati, inu akhoza kungoyankha akulozera manambala awo lomwe kupita Select mawu.

Tikukhulupirira kuti nkhani imeneyi udzapeza kudziwa zofunika za momwe ntchito mafunso SQL ndipo tsopano kusankha zofunika kuchokera Nawonso achichepere anu mosavuta.