remove duplicate rows based on one column value

Question

I have the below table and now I need to delete the rows which are having duplicate \"refIDs\" but have atleast one row with that ref, i.e i need to remove row 4 and 5. plea

Answer 1

This is similar to Gordon Linoff's query, but without the subquery:

DELETE t1 FROM table t1
  JOIN table t2
  ON t2.refID = t1.refID
  AND t2.ID < t1.ID

This uses an inner join to only delete rows where there is another row with the same refID but lower ID.

The benefit of avoiding a subquery is being able to utilize an index for the search. This query should perform well with a multi-column index on refID + ID.