Existing Null Values: If the column currently contains NULL values

Existing Null Values: If the column currently contains NULL values, you must either update those values to a non-null value or remove the NULL values before applying the NOT NULL constraint. SQL Server will not allow you to set a column to NOT NULL if there are existing NULL values in that column.

 

-- Update existing NULL values
UPDATE Employees
SET Email = '[e-mail]'
WHERE Email IS NULL;

SQL

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