check column exists in table and add column in one query
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I want check, exists or not in mytable column "auto", and if not exists, add his. a make this so:

      mysql-> SHOW COLUMNS FROM mytable 

after, with PHP I check, in result exists or not "auto" and if no, I make:

      mysql-> ALTER TABLE mytable  ADD auto  VARCHAR (30) NOT NULL COLLATE utf8_general_ci 


Question: please tell, how to make this in one query ?