主键是每行的唯一标识符，必须包含不重复的值，而且不能为空。

Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null.

youdao

主键是每行的唯一标识符，必须包含不重复的值，而且不能为空。

Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null.

youdao