Little brother. What is the purpose of the Design table field is not empty when we are building a database

What is the role of the Design table field when we are building the database?

Like this, when is the design null, and when does it have to be not null? Solving
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If it is not empty, it means that the field must have a value.

As to when the design is null, when does it have to be not null? It depends on the demand.
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Null empty value, indicating nothing
If the value of a field is optional in the business, then it can be set to NULL
Another use for NULL is that it can be used for input to a data item. This is important in situations where it takes more than one operation to form a complete record.
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Not empty, in MSSQL if the field does not have data to insert failure, MySQL seems to be strict mode will also fail. It is mainly used to constrain the integrity of the data.
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Mainly based on business scenarios, such as some field information is required, the user must fill in, otherwise it will prompt the operation failed.

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As if large data volume search, the field is not NULL search efficiency will improve, please God confirmed

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