MySQL error: Missing index for constraint

Question

I am creating 2 tables in my database:

DROP TABLE IF EXISTS `med_pharmacy`;
CREATE TABLE IF NOT EXISTS `med_pharmacy` (
  `med_pharmacy_id` int(11) NOT NULL          


        

Answer 1

The column referenced in a foreign key must be indexed. You need to add an index on medication.med_id. In fact, this should probably be the primary key of the table.

ALTER TABLE medication ADD PRIMARY KEY (med_id);

Answer 2

if you are giving

ADD CONSTRAINT `fk_med_pharmacy_medication1` 
FOREIGN KEY (`med_id`) 

A FOREIGN KEY constraint does not have to be linked only to a PRIMARY KEY constraint in another table; it can also be defined to reference the columns of a UNIQUE constraint in another table.

so med_id should have primary key in medication or reference the columns of a UNIQUE constraint