Modify column to change its length or nullability
修改列以更改其长度或可为空特性
The nullability characteristics of each column must be the same.
每列的为空性（nullability）特征必须相同。
Design attribute domain integrity. Considerations include CHECK constraints, data types, and nullability.
设计域完整性属性。考虑CHECK约束，数据类型和是否非空。
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