Cov txheej txheem:
Video: Yuav ua li cas yog tias koj sim tawm hauv qhov chaw tseem ceeb ntawm qhov chaw seem?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Yuav ua li cas yog tias koj sim tawm hauv qhov chaw tseem ceeb ntawm qhov chaw seem ? Kev nkag yuav tsis pub koj kaw lub database kom txog rau thaum tus nqi sau rau hauv.
Ntawm no, tus yuam sij tseem ceeb tuaj yeem khoob?
Taw qhia rau lub thawj tus yuam sij A thawj tus yuam sij yog ib kem ntawm kev sib txuas ntawm kab hauv ib lub rooj uas tshwj xeeb txheeb xyuas kab hauv lub rooj. A thawj tus yuam sij kem tsis tuaj yeem muaj NULL tus nqi lossis ib qho khoob txoj hlua. A thawj tus yuam sij tus nqi yuav tsum yog tshwj xeeb hauv tag nrho cov lus.
Dab tsi yog qhov tseem ceeb hauv kev nkag mus? A thawj tus yuam sij yog ib daim teb los yog txheej ntawm cov teb uas muaj nuj nqis uas txawv thoob plaws hauv lub rooj. Cov nqi ntawm cov tus yuam sij tuaj yeem siv los xa mus rau tag nrho cov ntaub ntawv, vim tias txhua cov ntaub ntawv muaj tus nqi sib txawv rau qhov tus yuam sij . Nkag mus txiav txim thawj tus yuam sij rau cov rooj tshiab hauv Nkag mus web apps thiab web databases.
Ib yam li ntawd, tib neeg nug, ua li cas koj tshem tawm tus yuam sij tseem ceeb hauv kev nkag?
Ua ntej peb nyem lub tsev tab thiab nyem qhov tab saib, thiab tom qab ntawd xaiv qhov tsim saib
- Xaiv cov roe uas nws tus yuam sij tseem ceeb tshem tawm.
- Ntawm Cov Tsim tab, hauv cov cuab yeej pab pawg, nyem qhov tseem ceeb.
- Qhov taw qhia tseem ceeb raug tshem tawm ntawm daim teb lossis cov teb uas peb tau teev tseg dhau los ua tus yuam sij tseem ceeb.
Dab tsi yog qhov ntsuas lossis qhov tseem ceeb tsis tuaj yeem muaj tus nqi null txhais tau li cas?
Qhov yuam kev " Index lossis tus yuam sij tseem ceeb tsis tuaj yeem muaj tus nqi Null ", tshwm sim thaum koj tau tawm ntawm thawj tus yuam sij ( qhov ntsuas ) teb khoob: Txhua lub rooj hauv Access database yuav tsum muaj a thawj tus yuam sij , thiab cov tus nqi tseem ceeb rau txhua cov ntaub ntawv yuav tsum muaj qhov tshwj xeeb.
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