What does COALESCE do in SQL?

In SQL Server (Transact-SQL), the COALESCE function returns the first non-null expression in the list. If all expressions evaluate to null, then the COALESCE function will return null.

SELECT COALESCE(NULL, NULL, 'ErcanOPAK.com', NULL, 'blog.ErcanOPAK.com');
Result: 'ErcanOPAK.com'

SELECT COALESCE(NULL, 'ErcanOPAK.com', 'blog.ErcanOPAK.com');
Result: 'ErcanOPAK.com'

SELECT COALESCE(NULL, NULL, 1, 2, 3, NULL, 4);
Result: 1

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