MySQL - 新增一列和查找主键

mysql> alter table mydate add column sex varchar(10);

mysql> alter table mydate add column name varchar(50) not null;

mysql> alter table mydate add column sal varchar(10) after name;

mysql> alter table mydate add column age varchar(10) first;

mysql> select count(*) primarynum from mydate md where md.bir='1999-10-10 00:00:00';
//结果大于等于1说明已经设置了主键。

mysql> alter table mydate drop primary key;

mysql> alter table mydate add primary key(bir);

show create table mydate;
//从列表中查看