版权声明:本文为博主原创文章,未经博主允许不得转载。 https://blog.csdn.net/czh500/article/details/85314148
mysql库和表的案例
直接po代码
#库和表的案例
USE shoppingCart;
#1.创建表dept1
/*
NAME NULL? TYPE
id INT(7)
NAME VARCHAR(25)
*/
#
CREATE TABLE dept1(
id INT(7),
`name` VARCHAR(25)
);
#
SELECT * FROM dept1;
#2.将表departments中的数据插入新表dept2中(可以跨库)
CREATE TABLE dept2 SELECT department_id, department_name FROM myemployees.departments;
#
SELECT * FROM dept2;
#
INSERT INTO dept1 SELECT department_id, department_name FROM myemployees.departments;
#
SELECT * FROM dept1;
#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 IF NOT EXISTS emp5(
id INT(7),
First_name VARCHAR (25),
Last_name VARCHAR(25),
Dept_id INT(7)
);
#
DESC emp5;
#
SELECT * FROM emp5;
#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;
#使用IF NOT EXISTS提高容错性
CREATE TABLE IF NOT EXISTS employees2 LIKE myemployees.employees;
#
DESC employees2;
#(仅仅复制了表的结构,没有复制数据)
SELECT * FROM employees2;
#
#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(30);
#
DESC emp5;
#
SELECT * FROM emp5;
#9.直接删除表emp5中的列test_column
ALTER TABLE emp5 DROP COLUMN test_column;
#
DESC emp5;
#
SELECT * FROM emp5;