![]() Instead, you must create the table without the constraint and then add it later with an ALTER TABLE statement. You cannot define a foreign key constraint in a CREATE TABLE statement that contains an AS sub query clause.There are a few things which you should know about the foreign key (Features of Foreign Key): While the constraint which involves more than one column in foreign key in the child table as well as more than one column in reference key in the parent table is called Composite Foreign Key. ![]() What Are Simple & Composite Foreign Key Constraints?Ĭonstraint which involves only one column in foreign key in child table and one column in reference key in parent table is called Simple Foreign Key. Similar to primary key constraint Foreign Key constraint is also of two types:
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