如何在mysql中使用父\u id选择随机？

我有这样的桌子

╔═════╦════════╦═════════════╗
║ id  ║  text  ║  parent_id  ║
╠═════╬════════╬═════════════╣
║   1 ║  test  ║           1 ║
║   2 ║  asd   ║           1 ║
║   3 ║  dsa   ║           1 ║
║   4 ║  fgh   ║           4 ║
║   5 ║  jkl   ║           4 ║
║   6 ║  kkk   ║           4 ║
║   7 ║  asas  ║           7 ║
╚═════╩════════╩═════════════╝

如何获得随机输出，如：

╔═════╦════════╦═════════════╗
║ id  ║  text  ║  parent_id  ║
╠═════╬════════╬═════════════╣
║   4 ║  fgh   ║           4 ║
║   5 ║  jkl   ║           4 ║
║   6 ║  kkk   ║           4 ║
║   7 ║  asas  ║           7 ║
║   1 ║  test  ║           1 ║
║   2 ║  asd   ║           1 ║
║   3 ║  dsa   ║           1 ║
╚═════╩════════╩═════════════╝

或

---

等等……

基于@sagi的ans进行轻微更新，增加了对组中行顺序的保证

SELECT *
FROM Table1
ORDER BY parent_id * rand()

这是演示

SQL: 输出：

---

您可以使用子查询来执行此操作，类似于以下解决方案：

SELECT s.* FROM YourTable s
INNER JOIN (select parent_id,max(rand()) as randVal FROM YourTable GROUP BY parent_id) t
 ON(s.parent_id = t.parent_id)
ORDER BY t.randVal

---

这将为每一组父id生成相同的rand值？@sagi我不这么认为。我在postgres上测试它，并生成非常随机的顺序。我想再次检查mysql，但sqlFiddle已关闭。但他需要它为每个父id生成相同的值。。不是完全随机的。哦，我没看到（@Megandi你可以更好地解释它，只是看看我所认为的都是随机值。我会修正它。但请阅读，这里是一个学习如何提高你的问题质量和获得更好答案的好地方。

ORDER BY t.randVal，s.id

是必需的。实际上不，它不是@dylansuth组中的顺序可能不再在ASC中。好的，还有不理解这个问题。每组将获得一个随机订单id。下次尝试创建美观的表

-- data
create table tbl(id int, text char(20), parent_id int);
insert into tbl values
(1 , 'test', 1 ),
(2 , 'asd',  1 ),
(3 , 'dsa',  1 ),
(4 , 'fgh',  4 ),
(5 , 'jkl',  4 ),
(6 , 'kkk',  4 ),
(7 , 'asas', 7 );
select * from tbl;

select t.* 
from tbl t inner join 
    (select parent_id, rand() rand_val from tbl group by parent_id) r
    USING(parent_id)
order by rand_val, id;

mysql> select t.*  from tbl t inner join      (select parent_id, rand() rand_val from tbl group by parent_id) r     USING(parent_id) order by rand_val, id;
+------+------+-----------+
| id   | text | parent_id |
+------+------+-----------+
|    7 | asas |         7 |
|    4 | fgh  |         4 |
|    5 | jkl  |         4 |
|    6 | kkk  |         4 |
|    1 | test |         1 |
|    2 | asd  |         1 |
|    3 | dsa  |         1 |
+------+------+-----------+
7 rows in set (0.00 sec)

mysql> select t.*  from tbl t inner join      (select parent_id, rand() rand_val from tbl group by parent_id) r     USING(parent_id) order by rand_val, id;
+------+------+-----------+
| id   | text | parent_id |
+------+------+-----------+
|    4 | fgh  |         4 |
|    5 | jkl  |         4 |
|    6 | kkk  |         4 |
|    1 | test |         1 |
|    2 | asd  |         1 |
|    3 | dsa  |         1 |
|    7 | asas |         7 |
+------+------+-----------+
7 rows in set (0.00 sec)

SELECT s.* FROM YourTable s
INNER JOIN (select parent_id,max(rand()) as randVal FROM YourTable GROUP BY parent_id) t
 ON(s.parent_id = t.parent_id)
ORDER BY t.randVal