Which one is the guideline of Referential integrity in a relationship ?

Question:Which one is the guideline of Referential integrity in a relationship ?

1.Do not enter a value in the primary key field of chield table if that value does not exist inthe primary key of the parent table

2.Do not enter a value in the foreign key field of a parent table if that value doesnot exist in the primary key of the child table

3.Do not enter a value in the foreign key field of a child table if that value does not exist in the primary key of the parent table

4.Do not enter a value in the foreign key field of child table if that value does not exist inthe foreign key of the parent table


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