7.8 ALTER TABLE syntax
      ALTER [IGNORE] TABLE tbl_name alter_spec [, alter_spec ...]
     alter_specification:
     ADD [COLUMN] create_definition [FIRST | AFTER column_name ]
     or ADD INDEX [index_name] (index_col_name,...)
     or ADD PRIMARY KEY (index_col_name,...)
     or ADD UNIQUE [index_name] (index_col_name,...)
     or ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}
     or CHANGE [COLUMN] old_col_name create_definition

     or MODIFY [COLUMN] create_definition
     or DROP [COLUMN] col_name
     or DROP PRIMARY KEY
     or DROP INDEX index_name
     or RENAME [AS] new_tbl_name
     or table_options