筆記:實現內連線
以運算元據庫tb_train_cpp2和tb_train_cpp22為例:
desc tb_train_cpp2;
desc tb_train_cpp22;
資料表tb_train_cpp2中的字段country與tb_train_cpp22中的字段cname對應[可實現內連線]
select tb_train_cpp2.username,tb_train_cpp2.age,tb_train_cpp2.position,tb_train_cpp22.people_num
from tb_train_cpp2
join tb_train_cpp22 on tb_train_cpp2.country=tb_train_cpp22.cname;
以運算元據表tb_train_user和tb_train_province為例:
desc tb_train_user;
desc tb_train_province;
select u.userid,u.username,u.score,p.proname
from tb_train_user as u
join tb_train_province as p on u.proid=p.id;
建立資料表tb_train_cpp31和tb_train_cpp32和tb_train_cpp33:
create table if not exists tb_train_cpp3(
userid tinyint unsigned key auto_increment,
username varchar(10) not null unique,
usercard char(5) not null,
proname varchar(10) default '四川-成都'
)engine=innodb charset=utf8;
insert tb_train_cpp3(username,usercard,proname) values
('呂布','10058','河南-信陽'),
('張頜','17744','四川-綿陽'),
('曹操','11684','遼寧-鞍山'),
('趙子龍','10892','江蘇-南京'),
('貂蟬','10906','湖北-武漢'),
('甘寧','12480',default),
('張遼','18745','安徽-合肥'),
('夏侯惇','19003','河南-開封'),
('左慈','19869','廣東-廣州'),
('趙飛燕','16891','湖南-岳陽'),
('張飛','12565','陝西-西安'),
('袁紹','12007','新疆-烏魯木齊');
create table if not exists tb_train_cpp33(
proname varchar(10) not null,
proid tinyint unsigned
insert tb_train_cpp33 values
('河南-信陽',12),
('四川-綿陽',25),
('遼寧-鞍山',38),
('江蘇-南京',44),
('湖北-武漢',50),
('四川-成都',28),
('安徽-合肥',69),
('河南-開封',17),
('廣東-廣州',72),
('湖南-岳陽',86),
('陝西-西安',99),
('新疆-烏魯木齊',105);
create table tb_train_cpp33(
username varchar(10) not null unique,
age int unsigned default 18,
*** enum('男','女','保密'),
ablity float(4,2)
insert tb_train_cpp33 values
('呂布',36,'男',78.24),
('張頜',32,'女',75.87),
('曹操',45,'男',94.66),
('趙子龍',default,'保密',90.18),
('貂蟬',24,'女',82.51),
('甘寧',28,'男',85.90),
('張遼',40,'男',89.02),
('夏侯惇',37,'保密',76.34),
('左慈',56,'女',91.48),
('趙飛燕',20,'女',88.63),
('張飛',48,'男',64.99),
('袁紹',50,'保密',76.89);
select t1.username,t1.usercard,t2.proid
from tb_train_cpp31 as t1
join tb_train_cpp32 as t2 on t1.proname=t2.proname;
select t1.username,t1.usercard,t3.age,t3.***,t3.ablity,t1.proname
from tb_train_cpp31 as t1
join tb_train_cpp33 as t3 on t1.username=t3.username;
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