How do you change the datatype of a column in SQL Server?

Question

I am trying to change a column from a varchar(50) to a nvarchar(200). What is the SQL command to alter this table?

Answer 1

For changing data type

alter table table_name 
alter column column_name datatype [NULL|NOT NULL]

For changing Primary key

ALTER TABLE table_name  
ADD CONSTRAINT PK_MyTable PRIMARY KEY (column_name)