浅析MysqlJoin语法以及性能改进(4)

+----+--------+------+--------+

|id|name|id|name|

+----+--------+------+--------+

|1|Pirate|2|Pirate|

|3|Ninja|4|Ninja|

+----+--------+------+--------+

2rowsinset(0.00sec)

求差集：

按照下面的举例可以求差集，如下：

复制代码代码如下:

SELECT*FROMALEFTJOINBONA.name=B.name

WHEREB.idISNULL

union

SELECT*FROMArightJOINBONA.name=B.name

WHEREA.idISNULL;

#结果

+------+-----------+------+-------------+

|id|name|id|name|

+------+-----------+------+-------------+

|2|Monkey|NULL|NULL|

|4|Spaghetti|NULL|NULL|

|NULL|NULL|1|Rutabaga|

|NULL|NULL|3|DarthVader|

+------+-----------+------+-------------+

四.Rightjoin

复制代码代码如下: