Case expression is not working properly in sql query

Question

I want to concat columns of supplier table with comma separator and put it into an alias field named \'contact\'. I have used cases for checking null values. Suppos

Answer 1

Use this

  SELECT supplier_Name, supplier_Address, supplier_reference, contact_Number1,
     contact_number2, contact_number3,
     case when contact_number2 is null then contact_number3 
          when contact_number3 is null then contact_number2 
          when contact_number3 is null and contact_number2 is null then '0'
          when contact_number2 is not null and contact_number3 is not null then contact_number2||','||contact_number3
     end as contact
  FROM SUPPLIER