空白の値を他の値に置き換えるSQL

select (CASE when (TelPhone IS NULL OR TelPhone='') then 'None' else TelPhone end) as TelPhone, (CASE when (Name is null or Name='') then 'None' else Name end) as name,(CASE when (CreateDate IS NULL OR CreateDate='') then 'None' else CreateDate end) as CreateDate,(CASE when ([Address] IS NULL OR [Address]='') then 'Not available' else [Address] end) as [Address] from User_Detail 

select if(age is null,18,age) from student

SELECT isnull(age,18) from Student

select coalesce(age,18) from student