ALTER [ONLINE | OFFLINE] [IGNORE] TABLE tbl_name
alter_specification [, alter_specification] ...
alter_specification:
table_options
| ADD [COLUMN] col_name column_definition
[FIRST | AFTER col_name ]
| ADD [COLUMN] (col_name column_definition,...)
| ADD {INDEX|KEY} [index_name]
[index_type] (index_col_name,...) [index_option] ...
....
以上命令可以在MySQL命令行中键入help alter或help alter table获得
很显然从语法上看，要么 ADD [COLUMN] col_name column_definition [FIRST | AFTER col_name ]
要么，ADD [COLUMN] (col_name column_definition,...)
加多个列的时候，无法 [FIRST | AFTER col_name ]