Video: Dab tsi yog qhov txawv ntawm ERD thiab schema?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Ob daim duab kos ua haujlwm zoo heev SIJ HAWM lub hom phiaj: ERD : kom ua rau cov neeg siv khoom tuag tag (thiab cov tswv lag luam) PAUB cov qauv ntawm kev daws teeb meem kev lag luam; thiab DATA SCHEMA : ib "blueprint" siv los ntawm DBAs los tsim cov ntaub ntawv, thiab los ntawm DEVELOPERS los siv cov ntaub ntawv hauv cov ntaub ntawv ntawd.
Dhau li ntawm qhov no, dab tsi yog schema hauv database?
Database schema . Lub sij hawm " schema " yog hais txog lub koom haum ntawm cov ntaub ntawv raws li ib tug blueprint ntawm yuav ua li cas lub database yog tsim (sib faib ua database rooj nyob rau hauv rooj plaub ntawm kev sib raug zoo databases ). Lub ntsiab txhais ntawm a database schema yog ib txheej ntawm cov qauv (cov kab lus) hu ua integrity constraints imposed on a database.
Tom qab ntawd, lo lus nug yog, qhov txawv ntawm schema thiab metadata yog dab tsi? Schema yog Layout ntawm koj Database. Piv txwv li, Cov Lus Teb, Lus Txhais, Nplooj Ntawv, Kab thiab kab thiab lwm yam Meta Cov Ntaub Ntawv yog cov ntaub ntawv hais txog koj cov Database. Piv txwv li, yog tias koj muaj cov ntaub ntawv hais txog tag nrho Rap Music, Koj cov ntaub ntawv meta yuav yog: Tus Sau, Tus naj npawb ntawm Cov Kab, Xyoo tso tawm, Qhov chaw, Lub npe Album, thiab lwm yam.
Xav txog qhov no, qhov txawv ntawm cov ntaub ntawv qauv thiab schema yog dab tsi?
Cov txawv yog a cov ntaub ntawv qauv piav qhia txog kev xav tau rau cov ntaub ntawv txhais cov ntsiab lus piav qhia thiab kev sib raug zoo, thaum a database , ib nrog schema los yog schemaless, yog cov cai uas siv kev khaws cia ntawm ib qho tshwj xeeb database platform.
Qhov txawv ntawm ER daim duab thiab ER qauv yog dab tsi?
Qhov yooj yim Qhov sib txawv ntawm E-R Model thiab Relational Qauv yog tias E-R model tshwj xeeb cuam tshuam nrog cov koom haum thiab lawv cov kev sib raug zoo. Ntawm qhov tod tes, Relational Qauv deals nrog Table thiab kev sib raug zoo nruab nrab cov ntaub ntawv ntawm cov rooj. Ib E-R Model piav qhia cov ntaub ntawv nrog qhov chaw teeb tsa, kev sib raug zoo teeb tsa thiab cov cwj pwm.
Pom zoo:
Dab tsi yog qhov txawv ntawm qhov sib txawv hauv zos thiab thoob ntiaj teb hauv SQL Server?
Qhov sib txawv hauv zos tau tshaj tawm hauv ib qho kev ua haujlwm whereas Ntiaj teb hloov pauv tau tshaj tawm sab nraum lub luag haujlwm. Cov kev hloov hauv zos tau tsim thaum lub luag haujlwm tau pib ua tiav thiab ploj thaum lub luag haujlwm xaus, ntawm qhov tod tes, Ntiaj teb hloov pauv yog tsim raws li kev tua pib thiab ploj thaum qhov kev pab cuam xaus
Dab tsi yog qhov sib txawv ntawm lub thawv thiab lub thawv ntawv thiab lub thawv ntawv yog dab tsi?
Ib lub thawv thiab cov ntawv nplawm (qee zaum hu ua boxplot) yog ib daim duab uas nthuav tawm cov ntaub ntawv los ntawm tsib lub ntsiab lus. Nyob rau hauv ib lub thawv thiab whisker zajlus: qhov kawg ntawm lub thawv yog lub sab sauv thiab sab quartiles, yog li lub thawv spans lub interquartile ntau yam. qhov nruab nrab yog cim los ntawm ib txoj kab ntsug hauv lub thawv
Dab tsi yog qhov txawv ntawm cov ntaub ntawv hom thiab qhov sib txawv?
Ib qho kev sib txawv yuav tsum muaj cov ntaub ntawv sib txuas nrog nws, piv txwv li nws tuaj yeem muaj cov ntaub ntawv xws li cov lej, lej lej, cov cim thiab lwm yam. Qhov sib txawv ntawm hom Integer khaws cov lej suav thiab tus cim typevariable khaws cov cim tus nqi. Thawj qhov sib txawv ntawm ntau hom ntaub ntawv yog lawv qhov loj me me
Dab tsi yog qhov zoo sib xws thiab qhov txawv ntawm relays thiab PLC yog dab tsi?
Relays yog electro-mechanical keyboards uas muaj coil thiab ob hom kev sib cuag uas tsis yog NO & NC. Tab sis Programmable Logic Controller, PLC yog lub khoos phis tawj me uas tuaj yeem txiav txim siab raws li qhov kev zov me nyuam thiab nws cov tswv yim & tso tawm
Dab tsi yog qhov sib txawv ntawm qhov ntsuas qhov ntsuas thiab qhov ntsuas thib ob?
Primary index: nyob rau hauv ib tug sequentially order file, qhov Performance index uas nws search key qhia cov sequential order ntawm cov ntaub ntawv. Kuj hu ua clustering index. Secondary index: ib qho Performance index uas nws qhov tseem ceeb tshawb nrhiav qhia qhov kev txiav txim sib txawv ntawm qhov kev txiav txim ntawm cov ntaub ntawv. Kuj hu ua non-clustering index