Computer, Zolwazi
SQL (Iintlobo data): Table
Kweli hlabathi lanamhlanje kukho inani elikhulu izixhobo kunye nobuchwepheshe yokugcina ulwazi. Enye yeendlela ezininzi zixhaphakileyo kuvimba, ngokuba ezisebenzisa iinkqubo zolawulo ezahlukeneyo. Le ndlela yokugcina icingela ukuba yonke idatha ngokucacileyo structured yaye adweliswe kwitafile ekhethekileyo. Nabo ke, kuba iimpawu zomhlathi uhlobo idatha ethile.
uhlobo data - ntoni na?
Namhlanje, kukho iingcaciso eziliqela, ucacisa ingqikelelo elithi 'uhlobo data. " Noko ke, ngamnye kubo Unengqondo omnye. Ngoko ke, uhlobo lwe data nga lokungavinjwa yonyulwa iqela data, luphawulwa imilinganiselo yayo (character, amanani, njl) kunye nemisebenzi isicelo amaxabiso ingqalelo.
Ububanzi iintlobo idatha ezininzi. Zisetyenziswa hayi kuphela ugcino, kodwa lwenkqubo ngemisebenzi eyahlukeneyo. Xa eyila iinkqubo uphuhliso yandile kunye nokusetyenziswa iindidi zedata lweenkobe kunye iseti ethile imisebenzi. Noko ke, ngokusekelwe umsebenzisi zisoloko iintlobo ezisisiseko data. SQL-standard kwakhona isekelwe nokusetyenziswa yeyona ixhaphakileyo ezisisiseko iintlobo, kodwa kukho inani add-ons ezithile.
Ukwahlukanisa iindidi zedata
data ngokwamaqela ngohlobo yaba ixesha elide yaye kubangelwa imfuneko lokuhlela ulwazi processing lula. Ke kaloku isiseko lweentlobo data ekhoyo benza ezimbini: umlinganiswa kunye yenombolo.
Ngenxa yokuhlelwa kwazo ngoku sele liphuhlise kubhaliwe, equka lathisi, ingqiqo, inani elipheleleyo, lencopho equkuqelayo yamanani kunye neentlobo string data. SQL - yokuhlela lugubungela ngokupheleleyo konke oku kungentla. Nangona kunjalo, kukho ezongezelelweyo wokongeza i-ngemvume ezinye DBMS zale mihla. Ezi ziquka Oracle and I SQL.
iindidi zedata Basic
Kusetyenziswa xa usenza amacwecwe nenkangeleko ukukhawulelana nemigangatho ulwimi SQL, iintlobo data zahlulwe iiklasi 4:
- strings;
- amaqhezu;
- value tselochiselennye;
- Umhla kunye nexesha swinene.
uhlobo data Umtya
Iqela lokuqala lwamaxabiso ukugcina nayiphi i data, emelwe njengabalinganiswa.
Kusenokuba abalinganiswa ezizodwa, amanani kunye neeleta, nto leyo ngokuphelela kwazo ziya kuthathwa njenge umtya na SQL umbuzo. Iintlobo Itheyibhile yeengcombolo kuluhlu oboniswe apha ngezantsi, ukwakha iqela lokuqala.
Char (ubukhulu) | Isetyenziswa ukugcina imitya. Ipharamitha kwi kwizibiyeli ivumela ukulungisa ubude bomtya egciniweyo. Ubukhulu eliphezulu kwi bytes anokuthi abekwe ngenxa mqolo - 255. |
VARCHAR (ubukhulu) | Ngokufanayo, uhlobo yangaphambili uyakwazi ukugcina umtya abalinganiswa 255 ubude. Nakuba kunjalo, ngokungafaniyo Char ukuba imali efunekayo bememori eyabelwe ukugcina ixabiso le hlobo. Oko kukuthi, ukuba leyunithi zabalinganiswa 5, bytes 6 inkumbulo efunekayo. Kwimeko yokuqala imemori xabiso ziya kukhethwa ngohlobo parameter utshilo. |
TEXT Tiny | Isetyenziswa ukulondoloza idatha umtya ukuya kutsho kwiimpawu ezili- 255. |
TEXT | Isetyenziswa okugcina ulwazi itekisi, ubukhulu apho engaphenduli ngaphezulu abalinganiswa 65 535. |
Blob | Uhlobo lwedatha uhlobo TEXT efanayo kwaye ivumela ukugcina ulwazi ledatha itekisi umthamo singabanga ukufikelela abalinganiswa 65.535. Kodwa xa kusenziwa isetyenziselwa ukugcina idata evakalayo, imifanekiso, amaxwebhu, njalo njalo. |
TEXT NCINCI | Uyilelwe ngokusekelwe kuhlobo lwesicatshulwa, kodwa ikuvumela ukugcina idatha ngenxa yobukhulu awongezelelekileyo ukuya ku 16.777.215 yoonobumba okanye iimpawu. |
Blob NCINCI | Isetyenziswa ukugcina kwidathabheyisi yamaxwebhu elektroniki, ubukhulu apho engaphenduli ngaphaya uphawu abalinganiswa 16.777.215. |
TEXT OMDE | Ezisebenza ngokufanayo uhlobo edlulileyo, kodwa ke umthamo memory esikhulu gigabytes ukuya ku-4. |
Blob OMDE | It ikuvumela ukuba ufake isiseko kwemithamo emikhulu data (4 294 967 295 abalinganiswa). |
ENUM (a, b, c, njalo njalo) | Uhlobo lwedatha ekhethekileyo esetyenziswa ukuchaza uluhlu lwamaxabiso kunokwenzeka. Kwe65535 Ikuvumela ukuba ukhankanye amaxabiso. Imiqolo uhlobo kuthethwa ukufumana ixabiso olunye elivela iseti ethile. Kwimeko apho Ukongeza ziya kuba amaxabiso ukuba zingekho kuluhlu enikwe kwi table iya kubhalwa ku inani engenanto. |
SET | Ichaza iseti imilinganiselo esebenzayo. Mu kuya kwa nshita uhlobo elidlulileyo, 64 kusetyenziselwa ziqulathe parameters enokuthi ukuqaliswa naziphi na okanye ezininzi ezakha yeseti iingxoxo. |
Table iindidi zedata iqhezu
iindidi zedata SQL iqhezu zisetyenziselwa ukugcina zokudada amanani ingongoma. Ukuziqhelisa, njengoko umthetho, wabeka izikhombisi zemali ezahlukeneyo. Kuxhomekeka ukuchaneka efunekayo usebenzise enye yezi zilandelayo zintathu:
Edadayo (ubukhulu, d) | Ivumela elinokuqukatha amanani iqhezu abonisa uvakalelo d. |
KABINI (ubukhulu, d) | Isetyenziswa ukugcina amanani iqhezu ngobuciko yokubini. |
IDESIMALI (ubukhulu, d) | Ukugcina amaxabiso iqhezu neengcingo. |
Ngokomzekelo, xa zokubhankisha ubalo ukuchaneka inxalenye iqhezu ufikelela ixabiso 8 okanye iimpawu 10-AYIKHO-Th. Iintlobo ezimbini zokuqala ayikwazi isetyenziswe kule ndawo.
Ukugcina izalathi zemali ngohlobo imigca lula kakhulu ngesisombululo iingxaki ezininzi. Nangona kunjalo, xa yokujongana nemiba yemali okanye zokwenza ukuguqulwa imisebenzi eyahlukeneyo SQL Uhlobo lwedatha kubaluleke kakhulu. Developers kufuneka uqiniseke ukuba siqwalasele uhlobo ukugcinwa kunye nokulungiswa neendlela, iinkcukacha sihlale efanayo.
Uhlobo lwedatha integer
Integers - iqela olwahlukileyo amanani oyinxalenye omnye iiklasi engundoqo. Iintlobo SQL data elipheleleyo zisekelwe phezu ukusetyenziswa lohlobo isiseko elipheleleyo kunye ukwandiswa iimpahla zazo.
INT (ubukhulu) | Ukugcinwa amaxabiso elipheleleyo oyinxalenye uluhlu [-2 31; 2 31 -1] |
TINYINT (ubukhulu) | Usebenzela amanani agcine uluhlu -128 ukuya 127 |
SMALLINT (ubukhulu) | Luphawulwa ukwanda uluhlu lwamaxabiso egcinwe mali ukususela -32 768 ukuya 32 767 |
MEDIUMINT (ubukhulu) | Isetyenziswa ukugcina amanani phakathi ledayimenshini -2 phambi Februwari 3 2 2 3 -1 |
BIGINT (ubukhulu) | Iquka uluhlu integers, ukususela nge-63 kunye nesiphelo -2 2 63 -1 |
Ukukhetha uhlobo ilungelo data, ungagcina okuninzi inkumbulo, inciphise neendleko ixesha umncedisi kufuneka-imibuzo SQL kubulawa. iindidi zedata, okanye mandithi kuluhlu lwabo, ukuqinisekisa ukuba isixa indawo yokubeka efunekayo.
Ngoko, ababhekisi phambili sedata kubalulekile ukukhumbula ukuba ukusetyenziswa kwe parameter ezinkulu iimpawu kukhokelela ekwandeni iindleko memory. Kuyimfuneko ukuba ukuhlalutya ngokucacileyo imisebenzi nokuchonga iimeko apho eyaziwa ayalingana kunye noluhlu iimeko amanani sebenzisa ezisayiniweyo. Ukuba uluhlu lwezimvo esetyenziswayo lincinane, yaye onke amanani ziya kuba HIV, bekuya kuba echanekileyo ngakumbi ukusebenzisa linga tyikitywanga sophawu wambumba ungatyikitywanga.
Iintlobo Umhla kunye nexesha data
Ekuhloleni iziseko iindidi zedata SQL, umhla kunye nexesha umdla ethile.
Ukusebenzisa ezi ntlobo zilandelayo inika iingenelo ezongezelelweyo kuphuhliso lweenkqubo ezixhomekeke iparameters okwethutyana.
DATE | Eyona njongo - umhla sibekwe ngendlela YEAR-INYANGA-USUKU ( "YYYY-MM-DD" okanye "yyyy-mm-dd"). Amaxabiso kamabonwakude zihlukaniswe "-", nangona kunjalo, nawuphi na umsebenzisi ngaphandle amanani esinokusetyenziselwa njengoko umahluli. |
TIME | It ikuvumela ukugcina amaxabiso iseli itafile okwethutyana. Konke okuxabisekileyo elikhankanyiweyo ifomati «hh: mm: ss» |
datetime | Luhlanganisa imisebenzi iintlobo ezimbini ezidlulileyo. Ifomati yokugcina ngolu hlobo lulandelayo: "yyyy-mm-dd hh: mm: ss». |
simiswe | Stores umhla kunye nexesha, inani axela lemizuzwana ukususela zobusuku 01/01/1970 ade ixabiso elichaziweyo. |
UNYAKA (M) | Isetyenziswa ukugcina amaxabiso yonyaka format ezimbini okanye ezine-engama. |
Yintoni enye kufuneka ukuba uyazi?
Zonke ezi ntlobo ze data systematized ngokucacileyo kwi-Microsoft. iindidi zedata SQL okungakanana phandle iinkcukacha ngakumbi.
Umzekelo, ayiqabe yi iinkcukacha, nokuba kusele imemori engakanani kwabelwa bytes usebenzisa uhlobo ngalunye. Emva kokuhlolisisa le nkcazelo ekhoyo, abaphuhlisi lula ukuba bayile isakhiwo iitafile kunye yonke database esekelwe izakhono iintsimbi womncedisi.
isalathisi Special - byte
Ngamanye amaxesha uphele ledatha ziye imeko apho xa udibanisa iingxelo etafileni into ebangela ukuba ufake iinkcukacha zonke kwiikholam engekhoyo. Ukulungiselela le njongo isalathisi ekhethekileyo inani engenanto - byte, nto leyo iyinto uncedo ekusebenziseni ulwimi SQL. Types of columns idatha, akunyanzelekanga ukuba ndizaliswe, xa kudalwa izithebe icaciswe umqhubi, ukuvumela ukufakwa amaxabiso null. umqhubi ngenye byte kunye isimaphambili ezongeziweyo TU abaqeshwe ukubonisa begqibezela olusisinyanzelo onke amaxabiso.
isalathisi byte Kuye akukho uhlobo, kodwa nje ubonisa ixabiso null kwi iitafile zesiseko sedata. Ngoko ke, oko zinokudityaniswa kunye nayiphi na kwezi ntlobo ngentla.
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