Elegant way to remove orphan rows?

Question

I have a table with a lot of history entries that contain customer IDs.

There is a separate customer table. Occasionally some of the customer entries are removed.

<

Answer 1

You could use cascading with foreign keys to accomplish this. In the following example, any time a row is deleted from A, or an A_ID in A is changed, this change will automatically be reflected in table B. You can read more on foreign keys in the MySql Documentation.

CREATE TABLE A(
   A_ID INT, 
   PRIMARY_KEY(A_ID)
) TYPE=InnoDB;

CREATE TABLE B(
   B_ID INT,
   A_ID INT,
   CONSTRAINT FK_B_A FOREIGN KEY REFERENCES A(A_ID) ON DELETE CASCADE ON UPDATE CASCADE,
   PRIMARY_KEY(B_ID, A_ID)
) TYPE=InnoDB;