Question

exampletable

+----+--------------------+------------------+
| id | name               | parent           |
+----+--------------------+------------------+
|  1 | menu1              | 0                |
|  2 | menu2              | 1                |
|  3 | menu3              | 0                |
|  4 | menu4              | 3                |
|  5 | menu5              | 0                |
|  6 | menu6              | 4                |
|  7 | menu7              | 4                |
|  8 | menu8              | 7                |
+----+--------------------+------------------+

我想在同一个表中选择没有子行。

感谢。

Answer 1

create table pc
(   -- parent child
    id int auto_increment primary key,
    name varchar(20) not null,
    parent int not null
);
insert pc(name,parent) values ('menu1',0),('menu2',1),('menu3',0),('menu4',3),('menu5',0),('menu6',4),('menu7',4),('menu8',7);

Select id,name from pc where id not in (select parent from pc)
+----+-------+
| id | name  |
+----+-------+
|  2 | menu2 |
|  5 | menu5 |
|  6 | menu6 |
|  8 | menu8 |
+----+-------+

Answer 2

这有点乱，但它会起作用：

SELECT t3.id,t3.name,t3.parent
FROM   test t3 
LEFT   JOIN (SELECT t1.id,t1.name,t1.parent from test t1 inner join test t2 on t1.id = t2.parent) t4 on t3.id = t4.id
WHERE  t4.id IS NULL;

输出：

+----+-------+--------+
| id | name  | parent |
+----+-------+--------+
|  2 | menu2 | 1      |
|  5 | menu5 | 0      |
|  6 | menu6 | 4      |
|  8 | menu8 | 7      |
+----+-------+--------+

mysql选择不存在同一个表中的子项

2 个答案: