If it is implemented, it means that the foreign key value from the table cannot exist independently. To show it in the table, you combine your "foreign key and id" and set it as the primary key. In this case.
When a foreign key triggers ondelete or onchange, it cannot be set to set null. Because the primary key "foreign key and id" of the slave table cannot have a null value (that is, the foreign key part of "foreign key and id" cannot be space-time)
Generally speaking, dotted lines are used for 1:1 and 1:n. It is better to use solid lines when n:m only represents the relationship between tables. Because the records in the main table disappear, relying on the corresponding relationship between the records is useless. If the corresponding relationship is not simply expressed, dotted lines should be used to meet the requirements.
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If it is implemented, it means that the foreign key value from the table cannot exist independently. To show it in the table, you combine your "foreign key and id" and set it as the primary key. In this case.
When a foreign key triggers ondelete or onchange, it cannot be set to set null. Because the primary key "foreign key and id" of the slave table cannot have a null value (that is, the foreign key part of "foreign key and id" cannot be space-time)
Generally speaking, dotted lines are used for 1:1 and 1:n. It is better to use solid lines when n:m only represents the relationship between tables. Because the records in the main table disappear, relying on the corresponding relationship between the records is useless. If the corresponding relationship is not simply expressed, dotted lines should be used to meet the requirements.