https://www.mssqltips.com/sqlservertip/6475/how-to-use-sql-server-coalesce-to-work-with-null-values/
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How to Use SQL Server Coalesce to Work with NULL Values
COALESCE is one of the tools you have in SQL Server to work with NULL values. It may not be the first one you think of, but it can be a very good choice. In this tip I will provide examples of how you can use COALESCE to peacefully coexist with NULL value