Why am I getting duplicate rows in SQL?
You are getting duplicates because more than one row matches your conditions.
To prevent duplicates use the DISTINCT keyword: SELECT DISTINCT respid, cq4_1, dma etc…
If you do not have duplicates in preweighting_data before then the only other chance is, that the column us_zip..
How do you prevent duplicate rows in SQL?
The go to solution for removing duplicate rows from your result sets is to include the distinct keyword in your select statement. It tells the query engine to remove duplicates to produce a result set in which every row is unique. The group by clause can also be used to remove duplicates.
What is duplicate row SQL?
Duplicate records in SQL, also known as duplicate rows, are identical rows in an SQL table. This means, for a pair of duplicate records, the values in each column coincide. Usually, we will retrieve duplicate data, when we are joining tables.
How do I count duplicate rows in SQL?
How it works:First, the GROUP BY clause groups the rows into groups by values in both a and b columns.Second, the COUNT() function returns the number of occurrences of each group (a,b).Third, the HAVING clause keeps only duplicate groups, which are groups that have more than one occurrence.
How do I find and delete duplicate rows in SQL?
SQL delete duplicate Rows using Group By and having clause In this method, we use the SQL GROUP BY clause to identify the duplicate rows. The Group By clause groups data as per the defined columns and we can use the COUNT function to check the occurrence of a row.