Add constraint foreign key

MySQL Add constraint foreign key

Add foreign key to MySQL table using alter table syntax and add constraint keyword.

MySQL Add constraint foreign key syntax

ALTER TABLE table_nameB ADD CONSTRAINT constraint_name FOREIGN KEY (column_name) REFERENCES table_nameA (column_name);

Add constraint foreign key example

ALTER TABLE `books` 
ADD CONSTRAINT fk_product_id 
FOREIGN KEY (product_id) 
REFERENCES `products` (id);

Output

table `books` altered.