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Most efficient way to remove duplicate rows

This script uses a hash join, the most performance efficient way of joining huge tables, to find duplicate rows.

This script uses a hash join -- the most efficient way of joining huge tables -- to find duplicate rows. It has been tested on Oracle 6.0 to Oracle 9i v2, and it works in all of those versions.

-- Set hash join enabled 
DELETE FROM <table> 
WHERE rowid IN 
  (SELECT t1.rowid 
   FROM   <table> t1, <same-table> t2 
   -- primary key is (a1, a2) 
   WHERE  t1.a1 = t2.a1 
     AND  t1.a2 = t2.a2 
     AND  t1.rowid < t2.rowid) 
/ 

Reader Feedback

Una S. writes: This one confuses me. If there is a prmary key on cols (a1, a2), how can there possibly be more than one row with the same values for a1 and a2 in the table to begin with?

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