Debugging duplicated data in SQL

All Posts
  1. Are you missing a GROUP BY clause?

  2. Check if your source tables or nested queries have duplicated rows. You’ll need to repeat steps 3 and 4 for every table or query result that contains duplicate rows.

    -- If the row_count is greater than 1,
-- you have duplicated rows in your results.

 SELECT
     < your_columns >,
     COUNT(*) AS row_count
 FROM
     < your_table_or_upstream_query >
 GROUP BY
     < your_columns >
 ORDER BY
     row_count DESC;
  3. Check your table to see how your join type interacts with your table relationships.
  4. Change your join type (LEFT JOIN, INNER JOIN etc) 
Date Added: