Question

I am trying to add NOT NULL and a DEFAULT to an existing table.

To do this, I am using a transitional table to populate any NULL values.

Table1 has the NULL column, Table2 has the improved design.

CREATE TABLE table1 (
    CustomerID INT
  , CartID NULL);

CREATE TABLE table2 (
    CustomerID INT
  , CartID NOT NULL DEFAULT NEWID());

INSERT INTO table2 (CustomerID, CartID)
SELECT CustomerID, CartID = CASE CartID WHEN NULL THEN NEWID() ELSE CartID END
FROM table1;

I still get the “Cannot insert the value NULL into column” error, even though I am populating every NULL value with a new value in the SELECT statement.

How can I make this work?

Answer 1

In SQL, NULL is not equal to NULL (and not unequal too).

“Does a dog have Buddha-nature or not?”
“NULL“

This is why CASE var WHEN NULL THEN … will never succeed.

Use this:

CASE WHEN CartID IS NULL THEN NEWID() ELSE CartID END

or just this:

COALESCE(CartID, NEWID())