A numeric field can be modified without error when added. Why?

gbagbcgb

A numeric field is fine when added
But if that field is empty when added (allowing nulls)
Then if the modification is still empty (that is, leave it blank), an error occurs.
why?
Is this my problem

gbagbcgb

It seems that the types do not match

恶魔右指

No, the landlord will try like this
update table name
set A column = null
where column A is null

gbagbcgb

It turns out that I did not add a null value when adding
So nothing went wrong
When modifying, those numeric types can't add such empty values.

wgfxman

Of course the number type cannot be ='' anymore