How to return count of duplicate values in a column? (SQL)

Question

I want a query to count the duplicate values in a column, e.g.,

total records=SELECT COUNT(column_name) FROM table_name;
distinct records=SELECT COUNT(DISTINCT column_name) FROM table_name;
duplicate count=total records-distinct records;

Answer 1

A simplification of the SQL you provided:

    SELECT Count(Column) - Count(DISTINCT Column)
    FROM   yourTable