MySQL - Error Code 1215, cannot add foreign key constraint

Question

i got these two succesfull queries:

create table Donors (
    donor_id int not null auto_increment primary key,
    gender varchar(1) not null,
    date_of_b         


        

Answer 1

In MySql, a foreign key reference needs to reference to an index (including primary key), where the first part of the index matches the foreign key field. If you create an an index on condition_code or change the primary key st that condition_code is first you should be able to create the index.