Question

I have a table of records, which has a self-relationship.

Additionally – to make searching easier – I have a flag which determines that a record has been referenced and hence that row is now “obsolete” and is only there for audit purposes:

CREATE TABLE Records
(
  RecordID INT(5) NOT NULL,
  Replaces INT(5) NULL,
  Obsolete INT(1) NOT NULL
)

RecordID is the PK, Replaces links to a previous RecordID which has now been replaced, and Obsolete is redundant information which just says that another record has replaced this one. It just makes searching a lot easier. The table is very large. These are just 3 of the columns.

The only problem is: there was a typo in one of the queries in the system so for a small set of rows, the Obsolete value was not set to 1 (true).

This query will show all the records with Obsolete equal to 0 which should be equal to 1:

   SELECT *
     FROM Records AS rec1
LEFT JOIN Records AS rec2
       ON rec1.Replaces = rec2.RecordID
    WHERE rec2.RecordID IS NOT NULL
      AND rec2.Obsolete = 0;

Now I need to run an UPDATE to change all those req2.Obsolete from 0 to 1, but I’m not sure how to write a query with an INNER JOIN.

Answer 1

You don’t need an inner join. Since your query already returns the records that need to be updated, just do this:

Update Records
set Obsolete=1 where
RecordID in (
 SELECT rec2.RecordID     
        FROM Records AS rec1
LEFT JOIN Records AS rec2
       ON rec1.Replaces = rec2.RecordID
    WHERE rec2.RecordID IS NOT NULL
      AND rec2.Obsolete = 0
)