How to delete duplicate rows in SQL Server?

Question

How can I delete duplicate rows where no unique row id exists?

My table is

col1  col2 col3 col4 col5 col6 col7
john  1          


        

Answer 1

With reference to https://support.microsoft.com/en-us/help/139444/how-to-remove-duplicate-rows-from-a-table-in-sql-server

The idea of removing duplicate involves

• a) Protecting those rows that are not duplicate
• b) Retain one of the many rows that qualified together as duplicate.

Step-by-step

• 1) First identify the rows those satisfy the definition of duplicate and insert them into temp table, say #tableAll .
• 2) Select non-duplicate(single-rows) or distinct rows into temp table say #tableUnique.
• 3) Delete from source table joining #tableAll to delete the duplicates.
• 4) Insert into source table all the rows from #tableUnique.
• 5) Drop #tableAll and #tableUnique