Video: Peb puas tuaj yeem ntxig ntau qhov NULL qhov tseem ceeb hauv qhov tseem ceeb Oracle?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Ntawd yog: Thaum (1, 1, null ) tso cai, tab sis tsis ntau tshaj ib zaug, ib kab nrog tus nqi ( null , null , null ) nyob rau hauv peb kab uas ua rau lub tus yuam sij tshwj xeeb raug tso cai txhua lub sij hawm - ib yam li hauv ib kab lus.
Kuj kom paub yog, Unique Key puas muaj ntau yam NULL qhov tseem ceeb hauv Oracle?
Vim Oracle qhov ntsuas ua tau tsis tuav NULL cov nqi , yog li nws txais ntau nulls . Nyob rau hauv cov ntaub ntawv ntawm Composite Cim ntawm ib lossis ntau kab, Txawm li cas los xij, ob kab uas muaj nulls rau ib los yog ntau tshaj tus yuam sij kab thiab tib ua ke ntawm tus nqi rau lwm tus tus yuam sij kem ua txhaum txoj cai.
Ib yam li ntawd, pes tsawg tus null tuaj yeem tso cai rau hauv tus yuam sij tshwj xeeb? ib null
Kuj Paub, peb tuaj yeem ntxig ntau qhov NULL qhov tseem ceeb rau tus yuam sij tshwj xeeb?
SQL Server: Tso cai Ntau tus nqi NULL hauv UNIQUE Kev txwv. Raws li ANSI, UNIQUE txwv tso cai ntau NULLs. Tab sis hauv SQL Server, nws tso cai xwb ib tus nqi NULL . Nrog rau UNIQUE kev txwv, koj ua tsis tau ntxig ntau NULLs.
Muaj pes tsawg null qhov tseem ceeb tuaj yeem muab tso rau hauv ib kem uas muaj kev txwv tshwj xeeb?
ib tus nqi NULL
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