How to add Foreign key to MySQL Table

If you already created a Table but you havent added foreign key constraint then you can do that by
running the following statement in MySQL

Run this before you run the FK Query Constraint

SET FOREIGN_KEY_CHECKS = 0;

Run the FK Query

ALTER TABLE tbl2Name 
  ADD CONSTRAINT fkConstraint FOREIGN KEY(fkcolumnName) 
      REFERENCES tbl1Name(pkcolumnName);

Run the below code again

 SET FOREIGN_KEY_CHECKS = 1;

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