SQL vakasiyana: tsananguro, mienzaniso, ehupfumi

Kazhinji kana ukashandisa SQL kuti dzosa umboo kubva matafura, inodzidzisa anogamuchira wandisa mashoko ndiwo kuvapo ane chose kufanana nouya pemitsara. Kuti tidzivise mamiriro ezvinhu aya, shandisa SQL akasiyana nharo iri mutongo Select. Nyaya ino ichakurukura mienzaniso kushandisa nharo ichi, uyewo ezvinhu umo application anofanira kusiyiwa ne nharo.

Tisati mberi kukurukura zvakananga mienzaniso, kusika Database kwaida kuchitsauko pamatafura.

gadziriro tafura

Chimbofungidzira kuti tine Database muzvitoro ruzivo pamusoro Wallpaper dzaitaurwa pamahwandefa maviri. Izvi tafura oboi (Wallpaper) ne ID minda (rakasiyana identifier), ari mhando (mhando Wallpaper -. Paper, vinyl, etc.), ruvara (ruvara), mumwe Struct (chimiro) uye mutengo (mutengo). Uye tafura Ostatki (residues) neminda id_oboi (a nezve yokukosha identifier tafura Oboi) uye count (nhamba mabhanzi aripo).

Muzadze date tafura. In patafura kuwedzera Wallpaper 9 zvinyorwa:

Tafura mapfupa - namapfumbamwe zvinyorwa:

We mberi kuti rondedzero akasiyana runyararo SQL.

Uise vakasiyana muna Select acho

akasiyana nharo igadzikwe pakarepo mushure Select guru iri queries. Akashandisa vose mbiru raanotaura mutongo Sarudza, nokuti achava kunze kwokupedzisira mubvunzo mugumisiro uri hungiso zvachose zvakafanana. Saka, kamwe zvakakwana tsanangurai paainyora SQL «sarudza akasiyana» chikumbiro. Kusara ndiko kushandiswa vakasiyana mukati uwandu hwezvinhu zvose zvabatanidzwa. mabasa kuti kutarisa zvishoma gare gare.

Zvinofanira kurangarirwa kuti dzakawanda Database uye asingauyi kuziva kwako mhando chikumbiro:

Hamuna vaiona nharo kakawanda kana kamwe wainyatsotaura, asi pamberi wechipiri, wechitatu kana mumwe mbiru vakasarudzwa. Uchawana chikanganiso kureva kukanganisa mu nemarongerwo.

Application vakasiyana queries mune mwero

Zviri pachena kuti zvakakodzera pakuvaka chivako pamatafura uye akazadza navo mukati chete tafura kunze mamiriro ezvinhu kana paine hungiso zvachose zvakafanana. Naizvozvo, mubvunzo kuurayiwa «Sarudza akasiyana *» pamwe wezvaizogona tafura imwe zvisingaiti.

Funga mamiriro ezvinhu apo tinofanira kuziva chii mhando tine Wallpaper, chete zvivanakire, kugadzirisa kubudikidza mhando:

Uye kuwana results:

Sezvinoonekwa mune tafura varipo nouya pemitsara. Kana isu wedzera dzaita Sarudza vakasiyana:

patinonyatsonzwisisa mugumisiro pasina kudzokorora:

Saka, kana zvakanaka kupinda mashoko ari tafura, ipapo pakarepo pashure foni kana kukumbira vatengi tinogona kupindura kuti mvura Wallpaper, Washington City Offices uye acrylic Wallpaper zvinowanikwa kuchitoro havasi. Kwakapiwa kuti kuwanda muzvitoro kazhinji hakungoitwi zana Wallpaper, vanoona mazita asiri nemamwe marudzi zvaizenge basa-nyanyisa.

Kushandisa vakasiyana uwandu hwezvinhu zvose zvabatanidzwa. mabasa mukati

SQL akasiyana nharo inogona kushandiswa chero uwandu hwezvinhu zvose zvabatanidzwa. ushande. Asi nokuti Min naMax chikumbiro chayo achava asina maturo, asi kana pakuverenga Verengai kana avhareji anokosha kusanganisira mamiriro ezvinhu apo hapana aizofanira kufungawo repetitions.

Ngatitii tinoda kuongorora inogona yokuchengetera zvinhu zvedu uye kutumira chikumbiro ichi, computes uwandu Coils aripo:

Chikumbiro agopa mhinduro 143. Kana, zvisinei, isu zvichachinja kuti:

tinowana zvachose 119, sezvo Wallpaper nokuti mugove nhamba 3 uye 7 vari kugutsikana zvakaenzana. Zvisinei, zviri pachena kuti mhinduro kwakaipa.

Most inowanzoshandiswa SQL akasiyana shanda Count. Saka, tinogona nyore kuwana mhando Wallpaper vangani akasiyana, tine:

Uye kuwana mugumisiro 5 - misi bepa uye kaviri-rukoko raive nebutiro uye vasiri dzakarukwa jira. Zvirokwazvo zvose akaona okushambadza yakadai: "chete tine siyana pamusoro 20 akasiyana Wallpaper," iro riri zvaireva kuti chitoro ichi hachisi nemudzimai gumi mabhanzi uye zvakasiyana-siyana Wallpaper mhando ano.

Zvinofadza kuti munguva iyoyo mubvunzo, unogona tsanangurai akawanda seizwi Count vanoti vakasiyana, uye pasina izvozvo. Ndizvo mamiriro ezvinhu chete apo zvakasiyana Select'e zvinogona wandei varipo nguva.

Kana kusiya kushandiswa nharo

Kubva kushandiswa SQL akasiyana nharo vanofanira nokusiiwa imwe nyaya mbiri:

1. Iwe kuita vakasarudzwa matafura uye vane chivimbo mune rakasiyana nekukoshesana. Panyaya iyi, kushandisa nharo hakuna kunaka, nokuti chimwezve mutoro pamusoro Server kana nemhosva (zvichienderana mhando DBMS).
2. Uri kutya kurasikirwa mashoko enyu. Regai titsanangure.

Ngatitii webasa anokumbira kuti nyora Wallpaper kuti, pamwe kunoratidza mbiru mbiri chete - ndezverudzii uye ruvara. Kubva tsika, iwe kupa nharo vakasiyana:

Uye - kurasikirwa vamwe mashoko:

Inogona kupa pfungwa yokuti pepa Wallpaper (kwakajairika uye hunyambiri-rukoko) hatina pfungwa imwe chete, chokwadi, kunyange zvedu tafura duku mbiri nyaya (kuitika pasina vakasiyana):

Naizvozvo, sezvo ari kunyora chero chikumbiro pamwe nharo akasiyana vanofanira kungwarira uye anokwanisa kusarudza chikumbiro chacho, zvichienderana basa.

nzira vakasiyana

Kusiyana nharo vakasiyana - nharo All. In kushandisirwa nouya mitsetse kuchengetwa. Asi sezvo default Database uye anowana kuti zvakakosha kuratidza zvose tsika, nharo All - ndiko kutoti qualifier pane chaiko basa nharo. Tinovimba kuti iwe zvino kunzwisisa kuti vakasiyana (SQL) rinoshandiswa. Description kukupa ruzivo rwakazara pamusoro feasibility kushandisa nharo iyi matambudziko akasiyana. Pashure pezvose, sezvo zvikazooneka, kunyange zvakadaro nyore nharo fomu yayo anovanza zvaioneka chaizvo zvinoita kurasikirwa Data uye kuratidza kururama ruzivo.