How can i make not allow column to allow null and Allow Null column to not allow null

Could any one help me to perform below task.

How can i make not allow column to allow null and Allow Null column t开发者_Go百科o not allow null.

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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