mysql 表的修改例题

#将departments表中的数据插入到dept2中

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

#将Last_name的长度修改为50

ALTER TABLE emp5 MODIFY COLUMN Last_name VARCHAR(50);

#根据表employees创建employees2

CREATE TABLE employees2 LIKE  myemployees.employees;

CREATE TABLE employees2
SELECT * FROM myemployees.employees;

#删除表emp5

DROP TABLE IF EXISTS emp5;

#将表employees2重命名为emp5

ALTER TABLE employees2 RENAME TO emp5;

#将表dept和emp5中添加新列test_column

ALTER TABLE emp5 ADD COLUMN test_column INT;
ALTER TABLE emp5 ADD COLUMN test_column INT; 

#删除表emp5中的列dept_id

ALTER TABLE emp5 DROP COLUMN  test_column;