Question

I’m currently having issue going through a test backup and restore of database table on my development machine for db2. Was never entirely successful. Although I was able to restore all data after a drop and re-create of the table, I wasn’t able to reset the foreign key constraint as I got SQL error complaining that keys don’t match. Here’s my exact steps, I’m sure not entirely the right way to do it, but it does eventually restore the 5423 rows of data:

The process

1. export to /export/home/dale/comments.ixf of ixf messages /export/home/dale/msg.txt select * from .comments

   Note: step 1 exports 5423 rows of data to a location

2. drop table .comments

3. import from /export/home/dale/comments.ixf of ixf create into .comments

   Note: step 3 here creates the table but does not insert any data rows

4. load client from /export/home/dale/comments.ixf of ixf modified by identityoverride replace into .comments

   Note: up until this step, I’m able to insert the 5423 rows of data in the recreated db table

5. alter table .comments add FOREIGN KEY (comments_id) REFERENCES .news (article_key)

   Note: here alter table fails as db2 complaints that some comments_id does not match article_key

Could anyone help with my problem here? Thanks in advance

Answer 1

The error means that some of the rows you IMPORT into the Comments table refer to rows that do not exist in the News table.

You might not be forming the constraint correctly. The column name “comment_id” sounds like the primary key to the Comments table. You want the foreign key, which matches the primary key of the News table. It might also be called “article_key” or “article_id”.

    ALTER TABLE Comments
      ADD FOREIGN KEY( article_key)
        REFERENCES News( article_key);

If “comment_id” is really not the primary key of the “Comments” table, then the problem comes from not backing up and restoring both the News and Comments table at the same time.

You can either EXPORT and IMPORT the News table along with the Comments table, or remove the Comments that refer to missing News rows with something like this

    DELETE FROM Comments
      WHERE comments_id NOT IN (
        SELECT article_key
          FROM News
      )

Before you do this, you might want to try listing the Comments which would be deleted by the above query

    SELECT * 
      FROM Comments
      WHERE comments_id NOT IN (
        SELECT article_key
          FROM News
      )