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

Code Example 1

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

Code Example 2

ALTER TABLE Customers
ADD Email varchar(255);

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 table_name

ADD column_name datatype;

Code Example 6

ALTER TABLE table
ADD COLUMN column VARCHAR (255) NOT NULL AFTER column;

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