Check out example codes for "sql server alter column". It will help you in understanding the concepts better.

Code Example 1

ALTER TABLE table_name
ALTER COLUMN column_name datatype;

Code Example 2

ALTER TABLE table_name 
ALTER COLUMN column_name new_data_type(size);

Code Example 3

ALTER TABLE Customers
ADD Email varchar(255);

Code Example 4

ALTER TABLE table_name

ALTER COLUMN column_name datatype;

Code Example 5

ALTER TABLE dbo.doc_exa 
ADD column_b VARCHAR(20) NULL, 
	column_c INT NULL ;

Code Example 6

ALTER TABLE table_name

DROP COLUMN column_name;

Learn ReactJs, React Native from akashmittal.com