alter table

ALTER TABLE Customers
ADD Email varchar(255);

ALTER TABLE table_name
ADD column_name datatype;

--example
ALTER TABLE Customers
ADD Email varchar(255);

ALTER TABLE table_name 
ALTER COLUMN column_name new_data_type(size);

ALTER TABLE table_name
ALTER COLUMN column_name datatype;

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

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

ALTER TABLE table_name
ADD column_name datatype;

ALTER TABLE table_name

ALTER COLUMN column_name datatype; 

ALTER TABLE nom_table
RENAME COLUMN colonne_ancien_nom TO colonne_nouveau_nom

ALTER TABLE table_name

ADD column_name datatype; 

-- With check if field already exists

IF NOT EXISTS(SELECT 1 FROM sys.columns 
          WHERE Name = N'Email'
          AND Object_ID = Object_ID(N'dbo.Customers'))
BEGIN    
	ALTER TABLE Customers
    ADD Email varchar(255);
END