Question

I am stuck with this error no 150 problem in mysql and I know there have been questions
which discuss this problem but I still can’t find where I am wrong. Here is the database I am trying to create:

create table business (
    ident varchar(40) NOT NULL,
    name varchar(50) NOT NULL,
    rating INT UNSIGNED NOT NULL,
    PRIMARY KEY(ident)
) ENGINE=InnoDB;

create table deals (
    business_id varchar(40) NOT NULL,
    deals_id varchar(20) NOT NULL,
    deals_title varchar(50) NOT NULL,
    PRIMARY KEY (business_id, deals_id),
    FOREIGN KEY (business_id) REFERENCES business(ident) ON DELETE CASCADE
) ENGINE=InnoDB;

create table d_options (
    business_id varchar(40) NOT NULL,
    dealid varchar(20) NOT NULL,
    option_title varchar(40) NOT NULL,
    PRIMARY KEY(business_id, dealid, option_title), 
    FOREIGN KEY(business_id) REFERENCES business(ident) ON DELETE CASCADE,
    FOREIGN KEY(dealid) REFERENCES deals(deals_id) 
) ENGINE=InnoDB;

I get error: ERROR 1005 (HY000): Can’t create table ‘test.d_options’ (errno: 150)

I know for foreign key constraints to be satisfied there should be a index in the parent table as per mysql documentation, but I think that there is by default indexing
on primary key.

The result of innodb status is:

120530  0:47:48 Error in foreign key constraint of table test/d_options:
FOREIGN KEY(dealid) REFERENCES deals(deals_id) 
) ENGINE=InnoDB:
Cannot find an index in the referenced table where the
referenced columns appear as the first columns, or column types
in the table and the referenced table do not match for constraint.
Note that the internal storage type of ENUM and SET changed in
tables created with >= InnoDB-4.1.12, and such columns in old tables
cannot be referenced by such columns in new tables.
See http://dev.mysql.com/doc/refman/5.1/en/innodb-foreign-key-constraints.html
for correct foreign key definition.

Any help is appriciated.

Answer 1

You have a compound primary key on (business_id, deal_id) and they are indexed as a pair, but to satisfy the FK, you need another index on deal_id alone:

create table deals (
    business_id varchar(40) NOT NULL,
    deals_id varchar(20) NOT NULL,
    deals_title varchar(50) NOT NULL,
    PRIMARY KEY (business_id, deals_id),
    FOREIGN KEY (business_id) REFERENCES business(ident) ON DELETE CASCADE,
    /* Add an index on deals_id, separate from the compound PK */
    INDEX idx_deals_id (deals_id)
) ENGINE=InnoDB;