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I'm getting around to cleaning a database but I need some help with deleting near duplicates in MySQL database but is only off by one character in a column. I've searched and found ways to remove true duplicates but each off the solutions I've seen for near duplicates (timestamp, deleting without worry about which record stays) don't seem to apply.

Certain data must remain based on one column.

id  |   plyrID |  year |  pos | teamID  
1   | 111548   | 2005  | OF   | 367  
2   | 111548   | 2005  | RF   | 367  
3   | 111548   | 2006  | RF   | 332  
4   | 592743   | 2012  | SS   | 99  
5   | 592710   | 2012  | SS   | 111  

If there is a near duplicate based on plyrID, year, and teamID and if pos = "OF", I want to keep the record where the pos is either "RF", "LF", or "CF". The result should look like:

id  |   plyrID |  year |  pos | teamID  
2   | 111548   | 2005  | RF   | 367  
3   | 111548   | 2006  | RF   | 332  
4   | 592743   | 2012  | SS   | 99  
5   | 592710   | 2012  | SS   | 111 

where the record with pos = "OF" is deleted and the other remains.

Any help would be much appreciated.

1 Answer 1

2

So, rephrasing your requirement a little, you want to delete every row whose pos has the value of OF and for which another row in the same table exists with the same plyrID, year and teamID, and with pos of RF, LF or CF.

That sounded almost SQL, you would only need to correct some "grammar":

DELETE FROM
  MyTable
WHERE
  pos = 'OF'
  AND EXISTS
  (
    SELECT
      *
    FROM
      MyTable AS t2
    WHERE
      t2.plyrID = MyTable.plyrID
      AND t2.year = MyTable.year
      AND t2.teamID = MyTable.teamID
      AND t2.pos IN ('RF', 'LF', 'CF')
  )
;

The above is standard SQL but it wouldn't work in MySQL. Needs rewriting with JOIN:

DELETE MyTable
FROM MyTable
  JOIN
      MyTable AS t2
    ON
      t2.plyrID = MyTable.plyrID
      AND t2.year = MyTable.year
      AND t2.teamID = MyTable.teamID
      AND t2.pos IN ('RF', 'LF', 'CF')
WHERE
  MyTable.pos = 'OF'
;
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  • 1
    Worked perfectly. Thanks for the quick help. Aug 4, 2015 at 2:09

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