Answers for "alter tables"

sqlserver add column to table

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

sql alter table

-- 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