查看表的定义

　　查看表的定义　　mysql> desc emp;　　| Field | Type | Null | Key | Default | Extra |　　| ename | varchar(10) | YES | | | |　　| hiredate | date | YES | | | |　　| sal | decimal(10,2) | YES | | | |　　| deptno | int(2) | YES | | | |　　4 rows in set (0.00 sec)　　8. 删除表　　mysql> drop table emp;　　Query OK, 0 rows affected (0.00 sec)　　9. 修改表　　mysql> desc emp;　　| Field | Type | Null | Key | Default | Extra |　　| ename | varchar(10) | YES | | | |　　| hiredate | date | YES | | | |　　| sal | decimal(10,2) | YES | | | |　　| deptno | int(2) | YES | | | |　　4 rows in set (0.00 sec)　　mysql> alter table emp modify ename varchar(20);　　Query OK, 0 rows affected (0.03 sec)　　Records: 0 Duplicates: 0 Warnings: 0　　mysql> desc emp;　　| Field | Type | Null | Key | Default | Extra |　　| ename | varchar(20) | YES | | | |　　| hiredate | date | YES | | | |　　| sal | decimal(10,2) | YES | | | |　　| deptno | int(2) | YES | | | |　　4 rows in set (0.00 sec)　　10. 删除表字段　　将字段age删除　　mysql> desc emp;　　| Field | Type | Null | Key | Default | Extra |　　| ename | varchar(20) | YES | | | |　　| hiredate | date | YES | | | |　　| sal | decimal(10,2) | YES | | | |　　| deptno | int(2) | YES | | | |　　| age | int(3) | YES | | | |　　+----------+---------------+------+-----+---------+-------+ 5 rows in set (0.00 sec)　　mysql> alter table emp drop column age;　　Query OK, 0 rows affected (0.04 sec)　　Records: 0 Duplicates: 0 Warnings: 0　　mysql> desc emp;　　| Field | Type | Null | Key | Default | Extra |　　| ename | varchar(20) | YES | | | |　　| hiredate | date | YES | | | |　　| sal | decimal(10,2) | YES | | | |　　| deptno | int(2) | YES | | | |　　4 rows in set (0.00 sec)　　11. 字段改名　　将age改名为age1, 同时修改字段类型为int(4)　　mysql> desc emp;　　| Field | Type | Null | Key | Default | Extra |　　| ename | varchar(20) | YES | | | |　　| hiredate | date | YES | | | |　　| sal | decimal(10,2) | YES | | | |　　| deptno | int(2) | YES | | | |　　| age | int(3) | YES | | | |　　mysql> alter table emp change age age1 int(4) ;　　Query OK, 0 rows affected (0.02 sec)　　Records: 0 Duplicates: 0 Warnings: 0　　mysql> desc emp　　-> ;　　| Field | Type | Null | Key | Default | Extra |　　| ename | varchar(20) | YES | | | |　　| hiredate | date | YES | | | |　　| sal | decimal(10,2) | YES | | | |　　| deptno | int(2) | YES | | | |　　| age1 | int(4) | YES | | | |　　5 rows in set (0.00 sec)　　12. 修改字段排列顺序　　将新增的字段birth date加在ename之后　　mysql> desc emp;　　| Field | Type | Null | Key | Default | Extra |　　| ename | varchar(20) | YES | | | |　　| hiredate | date | YES | | | |　　| sal | decimal(10,2) | YES | | | |　　| deptno | int(2) | YES | | | |　　| age | int(3) | YES | | | |　　5 rows in set (0.00 sec)　　mysql> alter table emp add birth date after ename;　　Query OK, 0 rows affected (0.03 sec)　　Records: 0 Duplicates: 0 Warnings: 0 　 郑州去胎记医院 http://www.zzzykdyy.com/　　mysql> desc emp;　　| Field | Type | Null | Key | Default | Extra |　　| ename | varchar(20) | YES | | | |　　| birth | date | YES | | | |　　| hiredate | date | YES | | | |　　| sal | decimal(10,2) | YES | | | |　　| deptno | int(2) | YES | | | |　　| age | int(3) | YES | | | |　　6 rows in set (0.00 sec)