The Select (SQL) statement

Shanduro yeSQL abbreviation (mutauro wemibvunzo yakarongwa yakarongeka) inoratidza kuti mibvunzo ndiyo inoshandiswa nguva dzose muSQL. Sarudza mitsetse inodikanwa, zvichinyanya kusanganisira data yakawandisa, kuputsa kana kurongazve mapuranga achabatsira Sarudza (SQL) - mutereri anoudza DBMS kuti ataure mamwe mashoko.

Operator Syntax

Kuti ushandise zvakakodzera chero mutengesi, iwe unofanira kutanga uzviziva nemashanduriro emutauro wepurogiramu mubvunzo. Apo patinotaura zvakananga pamusoro peSQL mutauro, Sarudza (operator) ine syntax inotevera:

Sarudza	Inotaurira dheseti kuti tiri kutumira chikumbiro chacho. Iri ndiro izwi guru.
One, two, three ...	Rongedzo yemakoromeri ekubudiswa
Kubva	Inoratidza zita retafura iyo kubva pakusarudza data. Ichowo chinhu chinokosha chinodiwa.

Iyi ndiyo inonzi "pfupi" syntax yomutengi, asi inoratidza kwatiri kuti kunze kweShoko rinokosha uye kubva kuDBMS, mhinduro yedu haizoiti.

Shanduro yakakwana yemuitirwo inoratidzwa mumufananidzo unotevera:

Pano, iyo Apo gwaro rinokubvumira kuchenesa kutsvaga nekutsanangura mamiriro.

Kuti uite maitiro ehutano uye shandisa huwandu hwebasa kwavari, Girasi nechikamu chinoshandiswa, uye kutsanangura mugumisiro mushure mekugadzirisa, sarudzo Zvave iko kushandiswa.

Rongedza nechakubvumira kuti usarudze hutsika hwemasarudzo akasarudzwa mukukwira kana kuburuka kurongeka.

с информацией: Kuti uwane kunzwisisa kunonzwisisika kweSarudzo, ngatimbofungidzira kuti mune dhesi redu pane mapoka etafura aya ane ruzivo:

Id	Bereka	Zita	Birthday	Muvara
1	Bobtail	Ishe	04/01/2017	Grey
2	Curl	Fint	03/16/2012	White
3	Mau	Panther	03/03/2017	Black
4	Bobtail	Tyson	02/23/2017	Grey
5	Burmilla	Athena	01/08/2017	Black

Mutsara mumwe nomumwe wetafura ine nhamba yakasiyana yekate, dzinza raro, zita rezita, zuva rekuberekwa nekuraira. Zvadaro, tichakurukura kuti sarudzo (SQL) inoshanda sei, zvichibva pane deta iri kubva petafura iyi.

Nhamba yakadini inotorwa kubva patafura

Sezvakakurukurwa pamusoro apa, mazwi emazwi anoshandiswa nguva dzose kusarudza mashoko akanaka kubva patafura.

Mushure meSarudza Chinyorwa, mapurumiti ekubudiswa anotsanangurwa. Iwe unogona kuita runyora rwemashoko anodiwa akaparadzaniswa nekomma, ipapo sarudzo yose ichaita seyiyi:

Sarudza ruvara, dzinza, zita Kubva kuKakati

Sezvaunogona kuona, tinogona kuronga mapuranga mumutemo wavanoda. Mukuwedzera, tinogona kuratidza chete mapuranga atinoda.

Iko kunewo mukana mutsva wekutarisa zvose mapuranga etafura. Kuti uite izvi, mushure mokunge Sarudza, imwe nyanzvi (*) inoratidzirwa ine nzvimbo. Iyo yose yakarongeka ichaita seyiyi:

Sarudza * Kubva kuKakati

Mugumisiro wemubvunzo wepamusoro ndeyeMatepa ose, iyo inomiririrwa sezvainoonekwa pakuguma kwechikamu chekupedzisira.

Vanhu vazhinji vanofarira nzira yekuisa mhinduro dzekuurayiwa muSQL Select mune tambo. Kazhinji kazhinji izvi zvinodiwa kana zvakakosha kubatanidza zita rezita, zita rokutanga uye zita remunhu uyu, rakagadzirirwa mune zvinyorwa zvisingatauri.

Mune mhaka yedu, tinobatanidza ukama uye ruvara rwekati kubva patafura Mapati. Iyo nuance ndeyokuti DBMS dzakasiyana siyana dzinoshandisa vanhu vakasiyana-siyana nokuda kwekutambira kugona. Mune zvimwe zviitiko, izvi zvinongowedzera (+), mune vamwe - mutsara wechipiri (||) kana ampersand (&), dzimwe nguva Concat operand inoshandiswa. Saka, usati wabatana, unofanirwa kuverenga rondedzero kune DBMS chaiyo yauri kushanda nayo.

Sarudza kubereka || ',' || Muvara Kubva kumakati

Chigumisiro chacho ndeichi:

Bereka, Ratidza

Bobtail, Grey

Curl, White

Mau, Black

Bobtail, Grey

Burmilla, Black

Husingabhadhari data yakasununguka

Kusiyana - basa Sarudza (SQL), iyo inobvumira kusabvisa kudzokorora kwemitsara yakafanana yakabva pamugumisiro wemuenzaniso.

Semuenzaniso, tinoda kuziva kuti ndeipi makati ari patafura yedu. Kana tikashandisa mubvunzo wakajeka:

Sarudza rudzi Kubva kuKakati

Kuti tichawana chikonzero chakatarisirwa:

Bereka

Bobtail

Curl

Mau

Bobtail

Burmilla

Sezvaunogona kuona, mbeu yeBobtail inodhindwa kaviri. Kupesana Kwepfungwa kuchagumisa kudzokorora, iwe unongoda kupedzisa mubvunzo:

Sarudza rudzi rwakasiyana Kubva kuKakati

Refinement yechikumbiro

Muzvokwadi, inenge pasina chero mhinduro dzemhinduro dzinoitwa sedheti yakakwana yematafura etafura. Ngatitarisei, mutongo upi muChitsuwa (SQL) unobvumira kugadzirisa zvirongwa zvekusarudza chete mitsara inodikanwa.

Ikoko ndiko. Muchirevo ichi, chirevo chinoshandiswa - kutaura kwakagadzikana kuchipa kukosha kweko "chokwadi" kana "nhema". Iyo Sarudzo inotsvaga inongotora chete iyo data kubva patafura iyo kutaura kwechimiro ichave Ichokwadi, kana kuti "yechokwadi."

Ichakubatsira kurongedza nemuumbi uyu shanduro iri nyore. Ngatiti tinoda kuziva zvose nezvekatsva.

Sarudza * Kubva kumakati Ikoko ruvara = 'Dema'

Mugumisiro wemubvunzo uyu uchava mitsara inotevera yetafura:

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

Iwe unogonawo kuwirirana nemamiriro ezvinhu uchishandisa Uye, Kana, Kwete manyolo mafambisi.

Gadzirira ne

Iboka nechisarudzo, chinoshandiswa muChitsuwa (SQL), chinokubvumira kuti uise mibvunzo nehuwandu hwekamuri imwechete (kana kuti mizamu), uye wozoshandisa basa rose kwavari.

Zvose zvinosanganisira:

• Nhamba - inotora nhamba yemitsara yakasarudzwa nemubvunzo.
• Sum ndiyo nhamba ye arithmeti yezvinhu zvose zvakasarudzwa zvikamu.
• Min - inonyanya kukosha kweiyo yakasarudzwa korombo maitiro.
• Max ndiyo iyo yakawanda yevakasarudzwa pamakorani maitiro, zvichienderana.
• Avg ndiyo yevhareji.

Chirongwa chechirevo ichi chinonyatsonzwisiswa pane muenzaniso wekrete. Ngatitaurei tinoda kuziva kuti vangani makakiti emarudzi ose atinayo. Kuti uite izvi, unofanirwa kuunza iyi inotevera mubvunzo wakaoma:

Sarudza chizvarwa, kuverenga (*) Kubva kumakati Girai nerudzi

Chigumisiro chekuurayiwa chichava tafura inotevera:

Bereka	Verenga
Bobtail	2
Curl	1
Mau	1
Burmilla	1

Sezvaunogona kuona, tine mabhuku maviri nema kittens, vamwe vose vane imwe chete. Mukuita, maererano nechikumbiro ichi, chinobva patafura yedu, mubereki anokwanisa kunzwisisa kuti ndeipi mhando dzemakati dziri kudiwa pakati pevatengi, uye izvo zvisiri.

Zvichida nokuti nekuda kwenhamba huru yezvinyorwa mufurafura chaiye, zvicharamba zvichidikanwa kutsanangura mubvunzo uye kubvisa chete zvizvarwa zvekitten, izvo zvisiri, somuenzaniso, gumi. Kuti uchenese kana kufungidza mapoka, shandisa Iva clause. Iko inokubvumira kudonha mamwe mapoka, akafanana neApi iyo ndima, iyo inorambidza mahwindo ega. Mamiriro acho anopiwa nehuwandu hwebasa. Tichawedzera mubvunzo:

Sarudza chizvarwa, kuverenga (*) Kubva kumakati Girai nerudzi Kuverenga (*) <= 10

Kubvira mamiriro ezvinhu atinoisa "nhamba yekittens yemarudzi ose haisi kupfuura 10", mugumisiro wacho wakafanana nemuenzaniso usina tsanangudzo. Asi pano zvakakosha kunzwisisa iyo purogiramu yebasa rekutsvaga Kuva. Asi kana tikashandura mamiriro ezvinhu anonzwisisika kuti Tive nhamba (*) = 1, ipapo mugumisiro wacho uchaderedzwa kusvika mitsara mitatu uye kubudisa kubereka kwekittens, iyo imwe chete yakasara.

Kuronga

Ngatitaurirane neArairo - -kutongwa kweApt (SQL) operator, iyo inokubvumira kuronga mitsara yemitambo kuburikidza nekuwedzera kana kuderedza maitiro mune imwe kana mamwe mapuranga.

Zvakakosha kuyeuka kuti Mutemo ndeye chirevo chokupedzisira chekuvaka kose kweShoko chirevo. Inoshandiswa mushure meKusarudza, Kubva, Kupi, Kundana,, Kuva.

Paunoronga, pane zvinhu zvitatu zvinokosha:

1) Unogona kutsanangura chero nhamba yehurukuro, imwe neimwe inogona kugadziriswa kana kukwira (ASC) kana kuburuka (DESC).

2) Zvose zvinyorwa zvakataurwa muChirongwa nemagwaro zvinofanira kunge zviripo pakati pehurukuro dzakasarudzwa muSarudzo.

3) Hazvina kudiwa kunyora mazita emamwe mazita mazita ekutsvaga, iwe unogona kungotsanangura mazita avo, pasi pavanoenda muSarudza chirevo.

Tinovimba kuti nerubatsiro rwechipiri ichi wakagamuchira ruzivo rukuru pamusoro pekushandisa SQL mibvunzo uye zvino iwe unogona nyore nyore kusarudza ruzivo rwakakosha kubva kuDBMS yako.