I have 3 tables: agreement, user, emails as follows and the id in user table is acting as a foreign key in email table(id(FK)) as well as agreement table id_two(FK).
I have referenced id(Foriegn Key) in emails table to id(Primary key) in user table using the below code successfully:
ALTER TABLE emails MODIFY COLUMN id INT NOT NULL,
ADD CONSTRAINT id
FOREIGN KEY(id)
REFERENCES user(id);
But i am getting an error #1022 - Can't write; duplicate key in table '#sql-13f0_30e'
when i execute the below query to refer id_two of agreement table to id(PK) of user table.
ALTER TABLE agreement MODIFY COLUMN id_two INT NOT NULL,
ADD CONSTRAINT id_two
FOREIGN KEY(id_two)
REFERENCES user(id);
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