无法添加外键约束

Question

My parent table creation is

create table product31
    (prod_id varchar(10), prod_name varchar(25))
    CHARACTER SET utf8 COLLATE utf8_unicode_ci

and my child table which want foreign key is

create table product32
    (prod_id varchar(10), prod_value varchar(25),
    constraint foreign key (prod_id) 
        references product31(prod_id) on update cascade on delete cascade)
    CHARACTER SET utf8 COLLATE utf8_unicode_ci

By running second table script i got error

cannot add foreign key constraint

plz help me

Answer 1

referenced field should be indexed in first table. So your create sysntax should be as per below-

CREATE TABLE product31 (prod_id VARCHAR(10),prod_name VARCHAR(25), KEY idx_prod_id(prod_id))CHARACTER SET utf8 COLLATE utf8_unicode_ci;

CREATE TABLE product32 (prod_id VARCHAR(10),prod_value VARCHAR(25), FOREIGN KEY pd (prod_id) REFERENCES product31(prod_id) ON UPDATE CASCADE ON DELETE CASCADE) CHARACTER SET utf8 COLLATE utf8_unicode_ci;

Note: If you keep your prod_id field as primary key then no need to create separate index as primary key already will be indexed.