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;