replacing null records with default records

Question

Dear Friends 

 

I Have three tables. I want to take all records from these tables. but in last records would be null or blank . In this condintion i want to replace those records with default value.I haven't idea how to fire sql query. Please help me.

 

----------------              ---------------------------      ---------------------------------------

Id | Name                  SudId | class |  ID            ImageId | Imagename | SudId

1  | ab         |              2        | A_2  |  1                1          |  ~/image/a    | 2

2  | sha      |               5        |   B4  |   2

 

my schema is like this and i want to display a default image if image is not in recard.

 

 

please help thanks