表名，列名等可能需要用反引号引起来，而不需要用撇号(')或双引号(").

Table names, column names, etc, may need quoting with backticks, but not with apostrophes (') or double quotes (").

ALTER TABLE subject
    CHANGE COLUMN `course_number`   -- old name; notice optional backticks
                   course_id        -- new name
                   varchar(255);     -- must include all the datatype info