MySQL-无法定义外键

Question

I'm trying to create tables on Wamp server using Python. There are two tables - person and message. The table message has a column person_id which should be a foreign key for table person.

After the tables are created, there is no foreign key in message table when I look at it via PhpMyAdmin. Is there something wrong with SQL queries?

Creation of person:

@staticmethod
def createTablePerson():
    return "CREATE TABLE IF NOT EXISTS person (" \
           "id INT NOT NULL AUTO_INCREMENT PRIMARY KEY," \
           "name VARCHAR(100)," \
           "surname VARCHAR(100)" \
           ");"

Creation of message:

@staticmethod
def createTableMessage():
    return "CREATE TABLE IF NOT EXISTS message (" \
           "id INT NOT NULL AUTO_INCREMENT PRIMARY KEY," \
           "personID INT NOT NULL REFERENCES person (id)," \
           "text VARCHAR(1000)" \
           ");"

Answer 1

MySQL parses but ignores “inline REFERENCES specifications” (as defined in the SQL standard) where the references are defined as part of the column specification. MySQL accepts REFERENCES clauses only when specified as part of a separate FOREIGN KEY specification.

Reference: http://dev.mysql.com/doc/refman/5.5/en/create-table.html

---

So, to add a foreign key constraint (for storage engines that support them), the foreign key has to be defined separately from the column.

With this, the REFERENCES clause is ignored:

personID INT NOT NULL REFERENCES person (id),

To have MySQL add a foreign key constraint, do it like this:

personID INT NOT NULL, 
...
FOREIGN KEY (personID) REFERENCES person (id),
...

Answer 2

You need to index the column before adding as foreign key. The commands should be as

CREATE TABLE IF NOT EXISTS person (
           id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
           name VARCHAR(100),
           surname VARCHAR(100)
  );

CREATE TABLE IF NOT EXISTS message (
           id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
           text VARCHAR(1000),
           personID INT NOT NULL,
           INDEX personid_idx (personID),
           FOREIGN KEY (personID)  REFERENCES person (id)

           );