Ib tus yuam sij tseem ceeb yog qhov tshwj xeeb kev sib raug zoo ntawm cov rooj sib tham (lossis kev sib txuas ntawm txhua kab) tsim los txheeb xyuas txhua lub rooj cov ntaub ntawvTus yuam sij tseem ceeb yog siv los ua tus cim tshwj xeeb kom nrawm nrawm cov ntaub ntawv hauv lub rooj. … Nws yuav tsum muaj tus nqi tshwj xeeb rau txhua kab ntawm cov ntaub ntawv. Nws tsis tuaj yeem muaj qhov tsis muaj nuj nqis.
Vim li cas tus yuam sij tseem ceeb siv hauv DBMS?
Ib tus yuam sij tseem ceeb yog kem lossis kab ntawv uas muaj qhov tseem ceeb uas txheeb xyuas txhua kab hauv lub roojLub rooj database yuav tsum muaj tus yuam sij tseem ceeb rau Optim rau ntxig, hloov kho, rov qab, los yog rho tawm cov ntaub ntawv los ntawm lub rooj database. Optim siv cov yuam sij tseem ceeb uas tau txhais rau hauv database.
Vim li cas peb thiaj txhais lub ntsiab tseem ceeb?
Lub hom phiaj tseem ceeb ntawm tus yuam sij tseem ceeb yog txhawm rau txheeb xyuas qhov tsis sib xws ntawm kab, qhov uas tus yuam sij tshwj xeeb yog txhawm rau tiv thaiv qhov sib npaug, hauv qab no yog qhov sib txawv ntawm thawj tus yuam sij thiab tshwj xeeb tus yuam sij. Primary Key: Tsuas muaj ib lub ntsiab tseem ceeb rau lub rooj xwb. Tus yuam sij tseem ceeb muaj ib lossis ntau kab.
Vim li cas tus yuam sij tseem ceeb yog qhov tshwj xeeb hauv database?
tus yuam sij tseem ceeb tswj hwm qhov tsis sib xws ntawm kab. Peb muaj peev xwm tsuas muaj ib qho tseem ceeb hauv lub rooj. Tus yuam sij tshwj xeeb tuaj yeem lees txais cov txiaj ntsig null. tus yuam sij tshwj xeeb tseem tswj hwm qhov tsis sib xws ntawm kab.
Puas yog tus yuam sij tseem ceeb ib txwm muaj?
Tus yuam sij tseem ceeb yog ib txwm muaj nyob hauv txhua SQL. Koj tsis tas yuav qhia meej meej tias nws yog UNIQUE. Ntawm ib sab: Koj tuaj yeem muaj ib tus yuam sij tseem ceeb hauv lub rooj thiab nws yeej tsis tso cai rau qhov muaj nuj nqis.
