How to return default value from SQL query

Question

Is there any easy way to return single scalar or default value if query doesn\'t return any row?

At this moment I have something like this code example:

Answer 1

If the query is supposed to return at most one row, use a union with the default value then a limit:

SELECT * FROM 
 (
  SELECT Name FROM Users WHERE Id = @UserId`
  UNION
  SELECT 'John Doe' AS Name --Default value
 ) AS subquery
LIMIT 1

Both the query and default can have as many columns as you wish, and you do not need to guarantee they are not null.