Pakati SQL: Mienzaniso Description

Kana uchishanda ndeyeukama Database umo mashoko anochengeterwa matafura, vanoshandisa tinowanzova nenguva basa zvakabudiswa tsika zvaisanganisira (zvisiri) mune imwe siyana. mutauro SQL kunoita kuti chaunoti kakawanda, izvo zvinofanira (havafaniri) nhengo kukosha akasiyana nzira - opareta In, Kufanana opareta, mubatanidzwa ezvinhu zvakawanda - zvishoma, uyewo SQL nokuda Between opareta. Description uye mienzaniso munyaya ino ichanyanya pamusoro azvino shanduro.

"Pakati" opareta mu SQL: nemarongerwo kurambidzwa

Panouya opareta pakati SQL uye kushandurwa - "mu pakati". Kushandiswa kwaro zvinoita kuti uise paunogumira "uye kubva" chimwe munda, uye kana rinotevera ukoshi chikawira mukati-siyana, ipapo Predicate achapiwa wakaiswa kuti "Chokwadi", uye mutengo achawira wokupedzisira mharidzo.

The nemarongerwo ari opareta zvikuru nyore:

Sezvaunogona kuona, mushure guru pakati unofanira kutaridzwa kukosha rezasi muganhu, ipapo UYE, uye yokumusoro muganhu.

Yokuverenga, chii mhando nemashoko ari opareta anogona kushanda pakati SQL:

1. With nhamba - integer uye fractional.
2. With mazuva.
3. With chinyorwa.

Ita ichi pakati SQL mashoko ane zvimwe dzose. We kuziva kwavari:

1. Kana tichishanda nhamba uye misi muganhu tsika "uye kubva" vanobatanidzwa mharidzo.
2. Lower Range kukosha anofanira kuva zvishoma pane rokumusoro muganhu, zvikasadaro hapana chichapiwa uratidzwe, nokuti mamiriro ezvinhu hachisi zvine musoro zvechokwadi. Special hanya anofanira kuva, kana, pane zvakananga tsika dziri ezvinhu variables vanobatanidzwa.

Kana tichishanda rugwaro kukosha yokumusoro siyana haina dziri mharidzo, kana isina kunorondedzerwa zvakarurama kwazvo. We funga ichi chikamu mune zvinotevera zvikamu zvakadzama.

Mharidzo nhamba uye misi mune imwe siyana

Tafura chete mashoko mamaneja, kushanda musangano. The tafura achava zvinotevera mamiriro:

Zadza tafura kubudikidza anotevera mashoko:

Vanoumba SQL mubvunzo pakati, izvo chichatibatsira kusarudza vose vashandi vane 2 kana 3 vana:

The Zvichaguma mitatu yamahwindo vane mashoko ari vashandi pamwe surnames Shumilin, Tropnikov uye Avdeeva.

Zvino sarudza vashandi vakagamuchira kubva 1 January 2005 kusvika 31 December 2016. Zvinofanira kucherechedzwa kuti Databases siyana nenzira dzakasiyana kubvumira kuti kunyora tichitaura yemichindwe. Kazhinji, zuva rehondo kuti chimiro zuva-mwedzi-gore (kana yamunenge) uye wakanyorwa chete kana kaviri prices. The DBMS MS Access Musi vanoumba chiratidzo "#". Mhanyai muenzaniso uyu chete anoritsanangura:

The Zvichaguma vashandi shanu basa panguva zvichibatanidzwa.

Next, ngationei kuti akunoita pakati SQL hungiso.

Kushanda pakati hungiso

A dambudziko zvakajairika chaizvo izvo zvinofanira kugadziriswa kana tichishanda mazita vashandi - ndiko kudikanwa asarudze avo vane mazita anotanga imwe tsamba chete. Uye tinoedza tongai mubvunzo uye vashandi vakasarudzwa mazita anotanga rokupedzisira zita kubva A kuti B:

Zvinoguma sezvinotevera:

Sezvaunogona kuona, vashandi vaviri vane zita iri tsamba B ari pamazita havana zvaisanganisira. Ndechipi chikonzero? Chokwadi ndechokuti chaizvo sei opareta anoenzanisa hungiso kuenzana. Line "B" rakapfupika tambo "Vinogradov" uye padded. Asi kana kufambira alphabetically dzezvimwe achava dzichimhanya vatambi, uye zita mharidzo haangavi kuwa. Databases siyana zvinopa dzakasiyana kugadzirisa dambudziko iri, asi kazhinji zviri nyore nzira kuratidza kuvimbika inotevera tsamba earufabheti iri kuwanda:

Kana kuurayiwa, asi mubvunzo mugumisiro uchatibatsira kugutsa zvachose.

nuance ichi chiripo chete kana kushanda hunhu data, asi rinoratidza kuti kunyange kana kushanda nyore zvakadai dzaishandisa sezvo pakati, unofanira kungwarira.