Ib tug yuam sij tseem ceeb yog ib tus yuam sij tshwj xeeb. Txhua lub rooj yuav tsum muaj feem ntau ntawm IB lub ntsiab tseem ceeb tab sis nws tuaj yeem muaj ntau tus yuam sij tshwj xeeb. Tus yuam sij tseem ceeb yog siv los txheeb xyuas cov kab lus sib txawv.
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.
Tus yuam sij txawv teb chaws tuaj yeem yog null?
By default tsis muaj kev txwv ntawm tus yuam sij txawv teb chaws, tus yuam sij txawv teb chaws tuaj yeem ua tsis tau thiab luam tawm. thaum tsim ib lub rooj / hloov lub rooj, yog hais tias koj ntxiv tej yam kev txwv ntawm uniqueness los yog tsis null ces tsuas yog nws yuav tsis cia lub null / duplicate tus nqi.
Tus piv txwv tseem ceeb yog dab tsi?
Ib tus yuam sij tshwj xeeb yog txheej ntawm ib lossis ntau tshaj ib daim teb / kab ntawm lub rooj uas tshwj xeeb txheeb xyuas cov ntaub ntawv hauv cov ntaub ntawv. Koj tuaj yeem hais tias nws me ntsis zoo li tus yuam sij tseem ceeb tab sis nws tuaj yeem lees txais tsuas yog tus nqi null thiab nws tsis tuaj yeem muaj qhov sib npaug.
Dab tsi yog qhov sib txawv ntawm qhov ntsuas thiab qhov tseem ceeb?
Tus yuam sij tseem ceeb yog qhov tshwj xeeb unique ntsuas. Tsuas yog ib qho tseem ceeb index tuaj yeem txhais tau hauv ib lub rooj. Tus yuam sij tseem ceeb yog siv los txheeb xyuas cov ntaub ntawv tshwj xeeb thiab raug tsim siv lo lus tseem ceeb PRIMARY KEY. Indexs tuaj yeem npog ntau kab ntawv, xws li index zoo li INDEX (columnA, columnB), uas yog qhov sib koom ua ke.
