SQL kupi: nzira kushanda uye mienzaniso

nokuti kushanda SQL Databases anonzi rimwe zvirongwa mitauro rakajairika. mutauro magadzirirwo haagoni chete kusika munhu Database, asi kushandisa nguva naye manipulations-siyana mashoko kuchinja kana mharidzo.

Kuti sarudza mashoko kubva Database uchishandisa Select design [date yakatarwa] kubva [patafura zita]. Zvakaitika zvinoratidza kuti muna 80% kuti zviitiko kushandiswa mune mashoko acho zvikumbiro vanofanira kushandisa dzakasiyana-siyana ezvinhu - pazviruva. Kuti aite izvi mutauro kuwedzera chikumbiro, ayo kunzwisisa, mamiriro ezvinhu hwakatangwa SQL-Where.

Nzira Use Where mamiriro

Kazhinji, programmer anofanira kusarudzwa anonyanya kupa mushumo, humboo anochengeterwa Database. Izvi zvingasava zvakakwana kuvaka nyore kufanosarudza mubvunzo. Kazhinji, unofanira kufungawo akasiyana-siyana ezvinhu, zvakabudiswa parameters, izvo zvinogona chaizvo chaizvo, kana kutarisa. kana date vari ataurwa siyana kana mune imwe tafura.

SQL-Where zvakagadzirwa zvinogona kushandiswa kugadza zvakabudiswa Data kana mamiriro kuti ritsigire panowanikwa mashoko vakatora kana kumativi tafura.

Apo kushandiswa pakururamisa ari zvakabudiswa parameters

Kana uchida tsanangurai zvimwe parameters yokusarudzira nhau Database, SQL-Where zvakagadzirwa nemarongerwo dzinogona kurongwa zvikuru nyore. Kuti aite izvi, unogona kushandisa mitemo zvinotevera:

1. Tinoda prostroen chikumbiro mureza kupfurikidza Select kubvira kuvakwa.

2. Takatsunga kushandisa kiyi Join hurongwa izvo matafura achaita chisarudzo.

3. With sechivako kupi akaisa mazita parameters kuitira muenzaniso.

mhando iyi chikumbiro iri nyore rokuvaka uye haakonzeri zvinetso kunyange beginners.

Kushandisa nemamiriro kuti ritsigire panowanikwa

Kana programmer tasked kwete chete kusarudza kubva mashoko pamusoro pemamiriro ezvinhu tafura, asiwo kuti atarise kundopinda yavo chete kana kupfuura matafura mumwe zano, SQL-Where zvakagadzirwa hunokosha.

With pakuvaka ichi, kuti nemarongerwo anogona kuvaka chete ezvinhu, asi pamwe nested queries, izvo zvichaita tarisa panowanikwa mitsara vakasarudzwa nenzira yakarongwa kuti rechitatu-party Database pamatafura.

Kazhinji, nokuti chinangwa ichi akaumba kwekanguva tafura kuti anonyora ose anodiwa, kuti asimbise panowanikwa munhu date yakatarwa.

Mienzaniso Use Where

Apo mienzaniso SQL achapiwa zvino. Ndakatanga kufungidzira kuti pane nematafura maviri pamwe date - Munzvandi uye TovarAmount. Muzana rokutanga, pane mazita vakatengesa zvinhu, mutengo, musi kutengeswa uye mutengi uyo yatenga chigadzirwa. In wechipiri akaratidza pamberi nhumbi, kana pane chii aripo.

Muenzaniso mumwe mubvunzo parameter, iro rinoti zvinhu zvose kutengeswa imwe mari mazuva achava mhando anotevera yokugadzirwa:

Sarudza kubva Munzvandi

Where T_Date> = '12 / 01/2016 'uye T_Date <=' '12 / 07/1016 uye T_PriceOut> 0

urongwa kwakadaro kuti mubvunzo anodzoka mazita zvigadzirwa, mashoko matafura, dzakanga dzatengeswa mumazuva manomwe December rokutanga, sezvinoratidzwa nemashoko mumwe zvakabudiswa ezvinhu: T_PriceOut> 0.

Kana tikafunga ezvinhu goho kwenhumbi dziri kudanda, kuvaka chirongwa chakadai achava:

Sarudza kubva Munzvandi

Where T_Tovar mu (sarudza TA_Tovar apo TA_ Amount> 0)

Nested mamiriro ari kupi pangava mazhinji, asi zvinokosha kutaura kuti zvimwe zvinhu zviri zvavakatemerwa, kwenguva refu zvichaita kumhanya mubvunzo. Ichi chaiva chikonzero kushandisa pfupi pamatafura. Zvikuru nokukurumidza kuti vaunze wandei izvi, uye ipapo enzanisa mashoko mavari, pane kuvaka mamiriro multiple kwevari date chivimbo chakasimba.