a query to remove duplicate rows from a table code example

Example 1: how to query without duplicate rows in sql

SELECT DISTINCT col1,col2... FROM table_name where Condition;

Example 2: query delete duplicates

DELETE FROM dups a USING (
      SELECT MIN(ctid) as ctid, key
        FROM dups 
        GROUP BY key HAVING COUNT(*) > 1
      ) b
      WHERE a.key = b.key 
      AND a.ctid <> b.ctid