标签：into 方便 pre 0.00 记录 class 结构 通过 select
为什么需要多表查询：
因为不可以把所有数据都放在一张表里
我们把不同数据存储 放在一张一张不同表 方便管理
但是数据还是一个整体，数据之间是有关联关系 那就要把分散的数据，合并到一起进行查询
多表查询概念：
通过连接方式，把有关系的表拼成一个整体，进行关联查询。
就是把多张表记录 合并到一张表去查询
新建数据库
create database db6 charset=utf8;
use db6;
#建表
create table department( id int, name varchar(20) ); create table employee( id int primary key auto_increment, name varchar(20), sex enum(‘male‘,‘female‘) not null default ‘male‘, age int, dep_id int );
#插入数据insert into department values (200,‘技术‘), (201,‘人力资源‘), (202,‘销售‘), (203,‘运营‘); insert into employee(name,sex,age,dep_id) values (‘mike‘,‘male‘,18,200), (‘alex‘,‘female‘,48,201), (‘jack‘,‘male‘,38,201), (‘yuanhao‘,‘female‘,28,202), (‘liwenzhou‘,‘male‘,18,200), (‘jingliyang‘,‘female‘,18,204) ;
#查看表结构和数据
mysql> desc department; +-------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | varchar(20) | YES | | NULL | | +-------+-------------+------+-----+---------+-------+ 2 rows in set (1.30 sec)
mysql> desc employee; +--------+-----------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +--------+-----------------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(20) | YES | | NULL | | | sex | enum(‘male‘,‘female‘) | NO | | male | | | age | int(11) | YES | | NULL | | | dep_id | int(11) | YES | | NULL | | +--------+-----------------------+------+-----+---------+----------------+ 5 rows in set (0.00 sec)
mysql> select * from employee; +----+------------+--------+------+--------+ | id | name | sex | age | dep_id | +----+------------+--------+------+--------+ | 1 | mike | male | 18 | 200 | | 2 | alex | female | 48 | 201 | | 3 | jack | male | 38 | 201 | | 4 | yuanhao | female | 28 | 202 | | 5 | liwenzhou | male | 18 | 200 | | 6 | jingliyang | female | 18 | 204 | +----+------------+--------+------+--------+ 6 rows in set (0.32 sec) mysql> select * from department; +------+--------------+ | id | name | +------+--------------+ | 200 | 技术 | | 201 | 人力资源 | | 202 | 销售 | | 203 | 运营 | +------+--------------+ 4 rows in set (0.00 sec)
标签：into 方便 pre 0.00 记录 class 结构 通过 select
原文地址：https://www.cnblogs.com/mingerlcm/p/9892371.html
