We all have written queries that use COUNT DISTINCT to get the unique number of non-NULL values from a table. This process can generate a noticeable performance hit especially for larger tables with millions of rows. Many times, there is no way around this. To help mitigate this overhead SQL Server 2019 introduces us to approximating the distinct count with the new APPROX_COUNT_DISTINCT function. The function approximates the count within a 2% precision to the actual answer at a fraction of the time. Let’s see this in action. In this example, I am using the AdventureworksDW2016CTP3 sample database which you can download here.  SET STATISTICS IO ON SELECT COUNT(DISTINCT([SalesOrderNumber])) as DISTINCTCOUNT…