How can I prevent a column from allowing null and allowing a column from Null to not allow null

Question

Can someone help me complete the below task.

How can I prevent a column from allowing null and allowing a column from Null to not allow null.

Answer 1

Use ALTER TABLE table_name ALTER COLUMN column_name datatype [NOT] NULL

Example:

 CREATE TABLE #Foo ( X INT NULL, Y INT NOT NULL ) /*This is metadata only change and very quick*/ ALTER TABLE #Foo ALTER COLUMN Y INT NULL /*This requires all rows to be scanned to validate the data*/ ALTER TABLE #Foo ALTER COLUMN X INT NOT NULL