mysql-库和表的管理

1.	创建表dept1
NAME	NULL?	TYPE
id		INT(7)
NAME		VARCHAR(25)


USE test;

CREATE TABLE dept1(
	id INT(7),
	NAME VARCHAR(25)
	

);
2.	将表departments中的数据插入新表dept2中

CREATE TABLE dept2
SELECT department_id,department_name
FROM myemployees.departments;


3.	创建表emp5
NAME	NULL?	TYPE
id		INT(7)
First_name	VARCHAR (25)
Last_name	VARCHAR(25)
Dept_id		INT(7)

CREATE TABLE emp5(
id INT(7),
first_name VARCHAR(25),
last_name VARCHAR(25),
dept_id INT(7)

);


4.	将列Last_name的长度增加到50

ALTER TABLE emp5 MODIFY COLUMN last_name VARCHAR(50);
#5.	根据表employees创建employees2

CREATE TABLE employees2 LIKE myemployees.employees;

6.	删除表emp5
DROP TABLE IF EXISTS emp5;

7.	将表employees2重命名为emp5

ALTER TABLE employees2 RENAME TO emp5;

8.在表dept和emp5中添加新列test_column，并检查所作的操作

ALTER TABLE emp5 ADD COLUMN test_column INT;
9.直接删除表emp5中的列 dept_id
DESC emp5;
ALTER TABLE emp5 DROP COLUMN test_column;