Makombiyuta, Databases
SQL (date mhando): Table
Munyika yanhasi pane vakawanda maturusi uye ruzivo kuti ruzivo chekuchengeta. Imwe rakajairika nzira ndiwo Database, nokuti iyo dzinoshandisa yakasiyana kuzvidzora enyika. Izvi yokuchengetera zvinhu nzira yokuti vose Data anonyatsooneka muronga uye akarongwa nenzira chaiyo tafura. Ivowo, ine yakananga date mhando chomupepanhau unhu.
date mhando - chii?
Nhasi, pane tsanangudzo dzakawanda, anotsanangura pfungwa rokuti "date mhando." Zvisinei, mumwe nomumwe wavo ane pfungwa. Saka, rudzi Data zvinogona pamadiro akasarudzwa sezvo humboo boka, dzinoratidzwa netsika dzayo (hunhu, Numeric, etc.) uye akavhiyiwa zvairevei vaiona tsika.
Yezvinoreva date mhando ndiyo chinoumbwa nezvinhu zvakawanda. Kushandiswa kwete chete nokuda kuchengetwa, asi mapurogiramu kuti mabasa akasiyana. Kana mazano zvirongwa wakapararira kukura uye kushandisa chizvarwa mashoko mhando ane chaicho vanochengeta remapazi. Zvisinei, kunobva mushandisi nguva dzose huru mashoko mhando. SQL-mureza iri inobva kushandiswa vakawanda mhando zvinokosha, asi ane vanoverengeka wakananga wedzera-Ons.
Kupatsanura pakati date mhando
Muzvikwata zvisina tsarukano date ne mhando yaiva yakareba uye anokonzerwa kudiwa kuronga mashoko nyore kugadzira. Zvino hwaro huripo date mhando vanoumba zviviri: hunhu uye Numeric.
Pahwaro zvavo kupatsanura ano pokuikurukura, izvo zvinosanganisira dzapiwa, nomusoro, integer, Numeric kuyangarara pfungwa uye tambo date mhando. SQL - kupatsanura zvachose anofukidza zvose pamusoro. Zvisinei, pane zvimwe wedzera-dzi vamwe DBMS ano. Ava vanosanganisira Oracle uye MySQL.
Basic date mhando
Used paaisika matafura hunhu kuti tisangane mutauro mitemo yacho SQL, mashoko mhando akakamurwa 4 makirasi:
- hungiso;
- zvikamu zviduku;
- tselochiselennye ukoshi;
- Musi uye nguva tsika.
Tambo date mhando
The boka tsika yokutanga kuchengeta chero data, achimiririrwa vatambi.
Zvinogona kuva inokosha vatambi, nhamba uye tsamba, izvo raora yavo kubatwa somunhu tambo chero mubvunzo SQL. Mhando date tafura Pachikamu riri pasi apa, kuti aumbe boka rokutanga.
KwaIsakari (saizi) | Rinoshandiswa yokuchengetera hungiso. Parameter ari mumabhuraketi anobvumira kugadzirisa urefu zvakachengetwa tambo. The kunonyanyisa kukura mune bytes anogona chigadzirirwe mutsara - 255. |
VARCHAR (saizi) | Saizvozvowo, rapfuura mhando anogona kuchengeta tambo 255 vatambi refu. Zvisinei, kusiyana kwaIsakari kuti zvaida huwandu ndangariro dzinounzwa kuchengeta kukosha ichi mhando. Kureva kuti tambo zvinosanganisira 5 vatambi, 6 bytes okuyeuka kunodiwa. Muchiitiko chokutanga kuyeuka kuti kukosha achapiwa kusarudzwa maererano akati parameter. |
duku TEXT | Kushandiswa chitoro tambo Data anosvika 255 vatambi. |
TEXT | Kushandiswa kuchengeta wenyaya ruzivo, kukura asingasvavi pfuura 65 535 vatambi. |
BLOB | The mhando mashoko akafanana TEXT mhando uye anobvumira kuchengeta Database chinyorwa mashoko ane inzwi kunogona kusvika 65.535 vatambi. Asi tsika rinoshandiswa kuti kuchengetera ekuteerera data, mifananidzo, zvemagetsi zvinyorwa, uye zvichingodaro. |
svikiro TEXT | Yakanga yakagadzirwa kwakavakirwa mhando TEXT, asi anobvumira kuti kuchengeta mamwe mashoko nokuda rakawedzera kukura kusvika 16.777.215 tsamba kana zviratidzo. |
svikiro BLOB | Inoshandiswa kuchengeta ari Database zvigadzirwa zvinyorwa, kukura asingasvavi kusapfuudza mucherechedzo 16.777.215 vatambi. |
REFU TEXT | Vakuru yakafanana yapfuura mhando, asi ane hombe ndangariro kukwanisa anosvika 4 gigabytes. |
REFU BLOB | Kunoitawo kuti aiswe mujinga guru zvemaBhaibheri Data (4 294 967 295 vanotaurwa). |
ENUM (a, B, C, etc.) | A chaiyo date mhando rinoshandiswa kurondedzera mazita zvichibvira tsika. 65535 Inokutendera tsanangurai tsika. Mitsara mhando iri mubvunzo vanogona kugamuchira chimwe ukoshi kubva yamunenge yakatarwa. In Kana apo Kuwedzera achava tsika dzisina kupa mu mazita anopiwa tafura achanyorwa kuti isina kukosha. |
Isai | Inorondedzera iine musoro tsika. Kusiyana zvapfuura mhando, 64 inoshandiswa dzine parameters kuti anogona initialized nechinhu kana akawanda okunze kubva yakatarwa kukakavadzana. |
Table fractional date mhando
Fractional SQL date mhando anoshandiswa kuchengeta zvinoyangarara pfungwa nhamba. In tsika, sezvo mutemo, akaisa siyana zviratidzi zvemari. Zvichienderana zvaida kururama kushandisa mumwe wevatatu zvinotevera:
Ichiyangarara (size, d) | Kunoitawo rine fractional nhamba anoratidza zvakarurama d. |
DOUBLE (size, d) | Unoshandiswa yokuchengetera fractional nhamba pamwe binary nemazvo. |
Grade (size, d) | Kuchengeta fractional tsika sezvo hungiso. |
Somuenzaniso, muna rwezvemabhengi kukarukureta rakarurama fractional chikamu chinosvika ane ukoshi 8 kana 10-kn-Th zviratidzo. nezvemarudzi maviri okutanga hazvigoni kushandiswa munzvimbo iyi.
Kudzora zviratidzi zvemari muchimiro mitsetse hwezvekukurukurirana zvikuru yokupedza matambudziko akawanda. Zvisinei, mukubata emari kana kuita siyana akavhiyiwa SQL Data mhando kutendeuka kwakakosha. Developers vanofanira kuva nechokwadi kuti funga mhando okuchengetera uye kubudiswa nzira, ari mashoko nguva dzose kuramba zvakafanana.
Integer date mhando
Integers - a yoga boka nhamba achiumba rimwe chinoumba makirasi. Integer SQL date mhando dzinobva kushandiswa pechingoro mhando INTEGER neimwe kuwedzerwa zvivako zvayo.
Int (saizi) | Storage integer tsika wezvamatongerwe zvakawanda [-2 31; 2 31 -1] |
TINYINT (saizi) | It kunoshanda chitoro nhamba iri kuwanda -128 kusvika 127 |
SMALLINT (saizi) | Dzinoratidzwa zvakawedzera siyana tsika mudura uwandu kubva -32 768 kusvika 32 767 |
MEDIUMINT (saizi) | Kushandiswa nekuchengeta nhamba pakati -2 divi pamberi February 3 2 2 3 -1 |
BIGINT (saizi) | Anofukidza kuwanda integers, uchitanga 63 uye kuzviuraya -2 2 63 -1 |
Kusarudza rworudyi mhando data, unogona kuponesa yakawanda ndangariro, uye kuderedza mari Server nguva inodiwa SQL-queries vari aurayiwe. date mifananidzo, kana panzvimbo yavo siyana, huwandu hunodiwa okuchengetera nzvimbo.
Naizvozvo, Database Developers Zvakakosha kuyeuka kuti kushandisa guru neeSultan unhu kunotungamirira kuwedzera achiyeukwa mutengo. Zvakakodzera pachena kuongorora mabasa uye kuziva zviitiko apo anozivikanwa anofungidzirwa siyana uye mamiriro ezvinhu kushandiswa vakasaina nhamba. Kana kuwanda nenharo inoshandiswa diki, uye vose nhamba vachava akanaka, zvingava zvakawanda dzakarurama kushandisa unsigned kuumbwa chizenga UNSIGNED.
The Mhando Musi uye nguva mashoko
Kudzidza nheyo SQL Data mifananidzo, zuva uye nguva vari kufarira.
Kushandisa marudzi anotevera zvinowedzera zvakwakanakira kukura hurongwa kuti kuvimba duku parameters.
DATE | Chinangwa chikuru - musi iiswe pamanyorerwo GORE-PAMWEDZI-DAY ( "YYYY-MM-dd" kana "yyyy-mm-dd"). Typical tsika dzakaparadzaniswa "-" Zvisinei, chero hunhu zvimwe pane nhamba anogona kushandiswa sezvo separator. |
TIME | Kunoitawo kuti achengetere sehofisi tafura sero tsika. tsika dzose dziri kutaurwa youduku «hh: mm: a» |
DATETIME | Chine mashandiro anoita yapfuura maviri marudzi. Kuchengetera nemanyorerwo ari sezvinotevera: "yyyy-mm-dd hh: mm: a». |
TIMESTAMP | Stores musi uye nguva, munhu countable nhamba mumasekonzi kubva pakatsaurirwa pakati pousiku 01/01/1970 uye kusvikira yamunenge ukoshi. |
GORE (M) | Kushandiswa achengetere wepagore tsika ari zviviri kana mana digit format. |
Chiizve unofanira kuziva?
Vose kwemarudzi aya mashoko vari systematized zvakadzama panguva Microsoft. SQL date mhando kwakashanda zvizere.
Somuenzaniso, kupendwa nokuda udzamu, sei ndangariro yakawanda dzinounzwa mu bytes vachishandisa mumwe mhando. Aongorora mashoko anowanika, Developers nyore kugadzira sechivako matafura uye yose Database kwakavakirwa Hardware nezvaanogona ari Server.
Special Pointer - null
Dzimwe nguva ndakapedza Database vane mamiriro ezvinhu apo paunenge kuwedzera zvinyorwa kuti tafura kudiwa kupinda mashoko muzvikamu zvose chinoshayikwa. Nokuti ichi chinangwa unokosha Pointer kuti isina kukosha - null, riri sechinhu chinoyamura kushandisa mutauro SQL. Mhando date yembiru, izvo hadzishandi kuti izare, paaisika matafura vari raanotaura ne opareta, kubvumira kwebasa rinofanira null tsika. Zvimwe null opareta ane mamwe chivakashure rirege vakashandisa kuratidza munhu fanira anopedza tsika dzose.
null Pointer Harina mhando, asi kungotaura anotaura null ukoshi ari Database pamatafura. Saka, unogona kuva pamwe chero apa marudzi.
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