mysql left join join right

標籤：

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 查兩個表的內才聯絡相同的值

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 左表的資訊全部會全部查出來  右表的資訊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 

mysql left join join right