Question

enter code here

My problem is this: in this database the junction table contains some rows where the kha_id and the icd_fk are the same. While it’s OK that kha_id appears in icd_junction more than once , it has to be with a separate icd_fk. I can run a query and get all of the ID#s and the codes which are listed more than once, but is there an industry-standard way of going about deleting all but one occurrence of each?

example: what i have is above

KHA_ID: 123456  V23 
        123456  V23
        123456  V24

I need one of the rows kha_id=123456 and ICD_FK=V23 taken out.

Answer 1

This:

DELETE j1
  FROM ICD_Junction AS j1
 WHERE EXISTS
        ( SELECT 1
            FROM ICD_Junction AS j2
           WHERE j2.KHA_ID = j1.KHA_ID
             AND j2.ICD_FK = j1.ICD_FK
             AND j2.ID < j1.ID
        )
;

will delete, for each KHA_ID and ICD_FK, all but one relevant row of ICD_Junction. (Specifically, it will keep the one with the least ID, and delete the rest.)

Once you’ve run the above, you should fix whatever code caused the duplication, and add a unique constraint to prevent this from happening again.

(Disclaimer: Not tested, and it’s been a while since I last used SQL Server.)

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Edited to add: If I’m understanding your comment correctly, you also need help with the query to find duplicates? For that, you can write:

SELECT KHA_ID,
       ICD_FK,
       COUNT(1)          -- the number of duplicates
  FROM ICD_Junction
 GROUP
    BY KHA_ID,
       ICD_FK
HAVING COUNT(1) > 1
;