SQL Server 检查约束可为空

Question

For any check constraint if the BOOLEAN_EXPRESSION returns true, then the CHECK constraint allows the value, otherwise it doesn't. For a null-able column, it's possible to pass null for this column, when inserting a row. When you pass NULL for the AGE column, the Boolean expression evaluates to UNKNOWN, and allows the value.But what will happen in case of a Non null-able column if I pass null ?

Answer 1

For any check constraint if the BOOLEAN_EXPRESSION returns true, then the CHECK constraint allows the value, otherwise it doesn't.

This is incorrect. A check constraint returns a check validation error only when the boolean expression evaluates to FALSE. NULL does not generate an error.

This is different behavior from WHERE and CASE WHEN clauses.

If the column is non-NULLable, then you will have a violation of the not- NULL constraint. I think that is checked before the CHECK constraint, but the ordering doesn't matter. You will get a nullability error.