how to find duplicate values in mysql?

To find duplicate values in a MySQL table, you can use the COUNT() function and the GROUP BY clause in a SELECT statement.

Here’s an example of how to find duplicate values in a MySQL table:

SELECT column_name, COUNT(*)
FROM table_name
GROUP BY column_name
HAVING COUNT(*) > 1;

In this example, we use the COUNT() function to count the number of occurrences of each value in the column_name column. We use the GROUP BY clause to group the rows by the column_name column, and we use the HAVING clause to filter the results to only include groups with a count greater than 1 (i.e., groups with duplicate values).

This will return a list of all the duplicate values in the column_name column, along with the number of occurrences of each value.

For example, if the table_name table contains the following data:

+------------+
| column_name|
+------------+
| value_1    |
| value_2    |
| value_3    |
| value_2    |
| value_3    |
| value_3    |
+------------+

Then the above SELECT statement will return the following

+------------+----------+
| column_name| COUNT(*) |
+------------+----------+
| value_2    |        2 |
| value_3    |        3 |
+------------+----------