CODEWITHSUNDEEP
sqloracle-database
user3074559
user3074559

Reputation: 1

Add Foreign Key to an existing column?

Hello i am beginner in SQL and i have one question:

How to add new Column_B(int) which is foreign key to an existing Column_A(id) in same Table_A?

I tried this but i got Error Code: 1215. Cannot add foreign key constraint

ALTER TABLE Table_A ADD COLUMN Column_B int;
ALTER TABLE Table_A 
ADD fk_Table_A FOREIGN KEY (Column_B) REFERENCES Table_A (Column_A);

Upvotes: 0

Views: 930

Answers (2)

Faisal Ashfaq
Faisal Ashfaq

Reputation: 2678

alter table Table_A 
  ADD constraint fk_Table_A FOREIGN KEY (Column_B) REFERENCES Table_A (Column_A);

Upvotes: 2

Haneev
Haneev

Reputation: 775

It is possible that your references does not match. It can only add a foreign key when all the rows satisfy the foreign key condition, which is in your case that every value of Column_B is in table_A.Column_A.

Upvotes: 0

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