SQL query:

ALTER TABLE  `blog` CHANGE  `id`  `id` BIGINT NOT NULL AUTO_INCREMENT

MySQL said: 

#1075 - Incorrect table definition; there can be only one auto column and it must be defined as a key

I am trying to create a blog, and I got the code done. Now, I need to make the id auto increase, but I get this error. Why am I getting this?

mysql sql mysql-error-1075
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