how to find duplicates oracle using nested select code example

Example 1: oracle finding duplicate records

SELECT column_name, COUNT(column_name)
FROM table_name
GROUP BY column_name
HAVING COUNT(column_name) > 1;

Example 2: how to delete duplicate rows in oracle

DELETE FROM your_table
WHERE rowid not in
(SELECT MIN(rowid)
FROM your_table
GROUP BY column1, column2, column3);