Foreign key created an extra column mySQL - mysql

Question

On of my foreign keys in a table within MySQL added an extra not null column labeled Customers_CustomerID, so I am not able to enter or update the table as required for my assignment. How can I fix this?

Answer 1

Several options. We could 1) drop the column 2) change the column to allow NULL values, 3) change the column definition to specify a non-NULL DEFAULT value for the column, 4) add a BEFORE INSERT trigger to set a non-NULL value to the column, 5) supply a valid value on an INSERT. Lot's of possibilities.
We could provide some additional assistance with the syntax for each of those options, but without the column definition, we can't give the exact syntax that would be required for adding DEFAULT value attribute.
It might not be possible to drop the column, if its used in an index or referenced in a foreign key constraint. The syntax to remove the column would be something like this:
ALTER TABLE mytable DROP customers_customerid ;
The syntax to change the column definition, would be something like this, to specify a DEFAULT value:
ALTER TABLE mytable CHANGE
customers_customerid customers_customerid BIGINT NOT NULL DEFAULT '1' COMMENT 'foo' ;
^^^^^^^^^^^
But we need to know the entire column definition, and repeat that, adding/changing just the bits that need to be changed. The statement above includes guesses about the datatype, et al.
We can get the current definition of the column from the definition of the table with a statement like this:
SHOW CREATE TABLE mytable;
Note: the statement to add a foreign key constraint doesn't add a column to the table. the statement(s) that you executed must have included syntax to add a column.

Answer 2

You haven't really defined what you're trying to fix. What do you mean by saying you are "not able to enter or update the table"? What tool are you trying to update it with?
Here's an example from the MySQL documentation on how you should create two tables and link them with a foreign key:
CREATE TABLE parent (
id INT NOT NULL,
PRIMARY KEY (id)
) ENGINE=INNODB;
CREATE TABLE child (
id INT,
parent_id INT,
INDEX par_ind (parent_id),
FOREIGN KEY (parent_id)
REFERENCES parent(id)
ON DELETE CASCADE
) ENGINE=INNODB;