Question

I am attempting to delete all rows in two dependent tables based on a third tables ID.

Table structure:

Transaction
-Transaction_ID (primary)
-Timestamp

Purchase
-Item_ID
-Transaction_ID
-Purchase_ID (primary)

Item
-Item_ID (primary)
-Client_ID

I would like to delete all rows from transaction/purchase that match the Client_ID in item. Sounds simple enough… even I can wrap my novice mind around that…

DELETE dbName.t FROM
  dbName.Transaction t
JOIN
  dbName.Purchase p
 ON
  p.Transaction_ID = t.Transaction_ID
JOIN
  dbName.Item i
 ON
  p.Item_ID = i.Item_ID
WHERE
  Client_ID = 1

Nope…

I get this error foreign key constraint fails... – I’m sure many of you are not surprised.

Is the issue that Purchase uses t.Transaction_ID? – (thus, this foreign key would fail)

OR is there likely other t.Transaction_ID dependent data in this table (i haven’t found any).

EDIT: COMPLETE ERROR

Cannot delete or update a parent row: a foreign key constraint fails
(`ItemTracker_dbo/Purchase`, CONSTRAINT `FK_Purchase_Transaction`  
FOREIGN KEY (`Transaction_ID`) REFERENCES `Transaction` (`Transaction_ID`) 
ON DELETE NO ACTION ON UPDATE CASCADE)

Answer 1

You can’t delete from a table as long as dependent records still exist in another table. In your case, the dependency goes like this

Transaction <- Purchase -> Item

So you need to delete any purchases first before you can delete transactions.

As an alternative to that two-step approach, I would recommend setting up an ON DELETE CASCADE constraint and go with this:

DELETE 
  Transaction 
WHERE 
  Transaction_ID IN (
    SELECT 
      Transaction_ID 
    FROM
      Purchase INNER JOIN Item ON Item.Item_ID = Purchase.Item_ID
    WHERE
      Item.Client_ID = <your Client ID here>
  )

Beware that this deletes any Transaction (and, through CASCADE, any Purchase) where there is a dependent Item with a matching Client_ID, regardless of whether there are any other items in it. If this is not what you want, the question needs to be refined.