IFNULL

• Returns an alternate value to be used in case the specified field doesn't exist or the value is NULL.
  • IFNULL(<fieldName>, <DefaultValue>)

  select IFNULL(Customer, "N/A")

• You can also specify an alternate column in place of an alternate value
  • IFNULL(<fieldName>, <fieldName2>)

  select IFNULL(CustomerId, CustomerName)