Quote:
Originally Posted by matrixmadhan
Basically, with combination of using selected columns ( column1 ) and the specific rowids ( rowid ), what is the need to specify an extra condition with a separate subquery to extract column1.
|
Yes you are right that it makes 2 sub-selects. If you have many duplicates, then your original post may be better. But suppose you only have a single duplicate. My subquery1 returns only a single value of column1 (the duplicate), where your subquery returns many values (the non duplicates). So now I have a single value to compare against tableA where you have many values. Yes, I still have to make subquery2, but it is against a much smaller set.
Subquery2 makes sure that, for a given value of column1, we don't delete the row with the smallest rowid.
