mysql left join join right

create table java (name varchar(255));
insert into java values ('java1'),('java2'),('blue'); create table mysql (name varchar(255)); insert into mysql values ('mysql1'),('mysql2'),('blue'); 

1.join 查詢 內聯查詢 查兩個表的內才聯系相同的值

select * from java join mysql as my on my.name = java.name; 

+------+------+
| name | name |
+------+------+
| blue | blue |
+------+------+
1 row in set (0.00 sec)查詢結果?

2.left join 外聯查詢 已左表為主表 左表的信息全部會全部查出來 右表的信息只有相關聯的才能查出來 剩下的查詢結果為null 效率慢一點

select * from java left join mysql as my on java.name=my.name;


+-------+------+
| name? | name |
+-------+------+
| java1 | NULL |
| java2 | NULL |
| blue? | blue |
+-------+------+
3 rows in set (0.00 sec) 查詢結果

3.rignt join 正好與left join 相反