/*join 建表語句*/
drop
database
ifexists test;
create
database test;
use test;
/* 左表t1*/
drop
table
ifexists t1;
create
table t1 (id int
notnull,name varchar(20));
insert
into t1 values (1,'t1a');
insert
into t1 values (2,'t1b');
insert
into t1 values (3,'t1c');
insert
into t1 values (4,'t1d');
insert
into t1 values (5,'t1f');
/* 右表 t2*/
drop
table
ifexists t1;
create
table t2 (id int
notnull,name varchar(20));
insert
into t2 values (2,'t2b');
insert
into t2 values (3,'t2c');
insert
into t2 values (4,'t2d');
insert
into t2 values (5,'t2f');
insert
into t2 values (6,'t2a');
mysql> select * from t1 join t2;t1.id = t2.id;
t1.id =t2.id;
t1.id = t2.id;
t1.id = t2.id
where t2.id
is null;
t1.id = t2.id
where t1.id
is null;
t1.id = t2.id
-> union
-> select * from t1 right join t2 on
t1.id = t2.id;
t1.id = t2.id
where t2.id
is null
-> union
-> select * from t1 right join t2 on
t1.id = t2.id
where t1.id
is null;
右表資訊全顯示，左表匹配左表id的資訊顯示
select * from t1 inner join t2 on t1.id = t2.id
兩表的交集，公共部分即兩表相同的 id 資訊顯示
select * from t1
union
select * from t2
t1和t2兩表資訊全顯示 但兩表需結構相同
select * from t1 right join t2 on t1.id = t2.id where t1.id is null;
匹配左表的資訊 全不顯示
select * from t1 left join t2 on t1.id = t2.id
union
select * from t1 right join t2 on t1.id = t2.id;
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