MySQL删除某些外键。

我有一张表，其主键用于多个其他表，并且有多个外键指向其他表。

CREATE TABLE location (
   locationID INT NOT NULL AUTO_INCREMENT PRIMARY KEY
   ...
) ENGINE = InnoDB;

CREATE TABLE assignment (
   assignmentID INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
   locationID INT NOT NULL,
   FOREIGN KEY locationIDX (locationID) REFERENCES location (locationID)
   ...
) ENGINE = InnoDB;

CREATE TABLE assignmentStuff (
   ...
   assignmentID INT NOT NULL,
   FOREIGN KEY assignmentIDX (assignmentID) REFERENCES assignment (assignmentID)
) ENGINE = InnoDB;

问题在于，当我试图删除其中一个外键列(即locationIDX)时，它会给出一个错误。

"ERROR 1025 (HY000): Error on rename"

如何在不出现此错误的情况下删除上面分配表中的列？