Question

I have create two tables with reference with another table:

I like this:

Table1:

CREATE TABLE species 
(
  id TINYINT NOT NULL AUTO_INCREMENT, 
  name VARCHAR(50) NOT NULL, 
  PRIMARY KEY(id)
) ENGINE=INNODB;

Table2 (Reference of the above table)

CREATE TABLE zoo 
(
  id INT(4) NOT NULL, 
  name VARCHAR(50) NOT NULL,
  FK_species TINYINT(4) NOT NULL, 
  INDEX (FK_species), 
  FOREIGN KEY (FK_species) REFERENCES species (id), 
  PRIMARY KEY(id)
) ENGINE=INNODB;

Than its automatically create an index for the FOREIGN KEY for FK_species in zoo table.

Now I am try to delete the Index of the zoo table:

ALTER TABLE zoo DROP INDEX FK_species;

Its showing the following MySQL error.

Error on rename of '.\test\#sql-1ec_9d' to '.\test\zoo' (errno: 150)

Answer 1

From FOREIGN KEY Constraints @ dev.mysql.com:

InnoDB supports the use of ALTER TABLE to drop foreign keys:

ALTER TABLE tbl_name DROP FOREIGN KEY fk_symbol;

If the FOREIGN KEY clause included a CONSTRAINT name when you created
the foreign key, you can refer to that name to drop the foreign key.
Otherwise, the fk_symbol value is internally generated by InnoDB when
the foreign key is created. To find out the symbol value when you want
to drop a foreign key, use the SHOW CREATE TABLE statement.