Question

I have a database table with many columns. Is there sql that will update records in that table where all or only specific columns are handled in such a way that if NULL is passed for any column value that the existing value not be changed?

---

Currently I can use solutions like these

UPDATE table
    SET column1 = COALESCE(@param1, column1),
        column2 = COALESCE(@param2, column2),
        ...
    WHERE id = @id

or

UPDATE table
set   column1 = isnull(@param1,column1),
      column2 = isnull(@param2,column2)

They both works well, though sometimes I want to explicitly save null in any column and I can’t do it with the above solutions. How?

Answer 1

One approach is to declare two parameters for each column, the first contains the value, the second is a bit instructs the query to insert null explicitly.

Example

create table example (column1 nvarchar(255), column2 nvarchar(255))

create procedure pUpdate(
    @column1 nvarchar(255)  = null,
    @nullColumn1 tinyint    = 0,
    @column2 nvarchar(255)  = null,
    @nullColumn2 tinyint    = 0
    ) as
    BEGIN
    
    update example 
        set column1 = Case When @nullcolumn1 = 1 
                           Then NULL ELSE IsNull(@column1, column1) End
        set column2 = Case When @nullcolumn2 = 1 
                           Then NULL ELSE IsNull(@column2, column2) End

    END

Then when calling from code, you only have to pass the parameters that you know need updating, or explicitely set the @nullcolumn to force a null.