三种数据库的SQL差异

==mysql==
alter table api_user change column a aaa varchar(500);
alter table api_user modify column b varchar(500);

==oracle==
alter table t_test_role rename column newcname to name
alter table t_test_role modify(name varchar(255));

==sqlserver==
alter table Table1 alter colunm column1 varchar(255)
alter table tablename alter colunm a abc varchar(255)