将FULL OUTER JOIN 转成left join，right join 和 union
select * from A
ID NAME
4 Spaghetti
1 Pirate
2 Monkey
3 Ninja
select * from B
ID NAME
3 Darth Vade
1 Rutabaga
2 Pirate
4 Ninja
SELECT dbo.A.id, dbo.A.name, dbo.B.id, dbo.B.name FROM dbo.A FULL OUTER JOIN dbo.B ON dbo.A.name = dbo.B.name
select dbo.A.id, dbo.A.name, dbo.B.id, dbo.B.name from dbo.A LEFT OUTER JOIN dbo.B ON dbo.A.name = dbo.B.name
union
select dbo.A.id, dbo.A.name, dbo.B.id, dbo.B.name from dbo.A right OUTER JOIN dbo.B ON dbo.A.name = dbo.B.name
select dbo.A.id, dbo.A.name, dbo.B.id, dbo.B.name from dbo.A LEFT OUTER JOIN dbo.B ON dbo.A.name = dbo.B.name
union all
select dbo.A.id, dbo.A.name, dbo.B.id, dbo.B.name from dbo.A right OUTER JOIN dbo.B ON dbo.A.name = dbo.B.name WHERE dbo.A.id IS null
这三个查询结果都是一样的
| id1 | name1 | id2 | name2 |
| 1 | Pirate | 2 | Pirate |
| 2 | Monkey | NULL | NULL |
| 3 | Ninja | 4 | Ninja |
| 4 | Spaghetti | NULL | NULL |
| NULL | NULL | 1 | Rutabaga |
| NULL | NULL | 3 | Darth Vade |
sql join的区别参考 https://www.cnblogs.com/logon/p/3748020.html