Video: Puas yog NULL hloov Oracle?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Taw qhia rau Oracle NVL() ua haujlwm
Cov Oracle NVL() muaj nuj nqi tso cai rau koj hloov null nrog rau qhov muaj txiaj ntsig ntau ntxiv hauv cov txiaj ntsig ntawm cov lus nug. NVL() muaj nuj nqi lees txais ob qhov kev sib cav. Yog Oracle tsis tuaj yeem implicitly hloov ib hom ntaub ntawv mus rau lwm qhov, ces nws teeb meem yuam kev.
Tib neeg kuj nug, yog NULL Oracle muaj nuj nqi?
The NVL muaj nuj nqi tso cai rau koj hloov null tus nqi nrog tus nqi pib. Yog hais tias tus nqi nyob rau hauv thawj parameter yog null , cov muaj nuj nqi rov qab tus nqi nyob rau hauv qhov thib ob parameter. Peb paub tias COL1 hauv lub rooj xeem muaj null hauv txhua kab tsuas yog thawj. Siv NVL muaj nuj nqi peb hloov lub null tus nqi nrog 'ZERO'.
Ib yam li ntawd, puas yog null vs Isnull? Yog Null thiab IsNull () ob leeg nrhiav null muaj nuj nqis, tab sis koj yuav tsis siv lawv tib txoj kev. Koj yuav siv Yog Null thiab Tsis yog Null hauv query expressions thiab SQL WHERE clauses. IsNull (), ntawm qhov tod tes, yog Visual Basic for Applications (VBA) muaj nuj nqi thiab tsuas yog siv hauv VBA modules xwb.
Raws li txoj cai, koj yuav hloov qhov null li cas?
Muaj ob txoj hauv kev hloov NULL nrog qhov tsis muaj nuj nqis hauv SQL Server, ua haujlwm ISNULL() thiab COALESCE(). Ob leeg ua haujlwm hloov tus nqi koj muab thaum qhov kev sib cav NULL e.g. ISNULL(kem, '') yuav rov npliag Txoj hlua yog tias tus nqi kab yog NULL.
Vim li cas NVL siv hauv Oracle?
Oracle NVL function Ua NVL muaj nuj nqi yog siv hloov NULL qhov tseem ceeb los ntawm lwm tus nqi. value_in yog qhov ua haujlwm los ntsuas ntawm qhov tsis muaj nuj nqis. Tus nqi_in teb tuaj yeem muaj datatype char, varchar2, hnub tim lossis tus lej datatype.
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