SQL statement to view duplicate data in a table

Introduction: We recently found a highly cost-effective SQL statement. When creating a primary key, it sometimes fails because the selected primary key column contains duplicate data, in this way, the primary key cannot be successfully created. At this time, we need to delete duplicate data. If there is a small amount of data, we can see it directly. But what if there is a large amount of data, then we need the following SQL statement. We can intuitively see which data is duplicated and how much data is duplicated.

The SQL statement is as follows:

Select column1, column2, count (*) from tableName

Group by column1, column2

Having count (*)> 1

Order by count (*) desc