mysql buglist上关于SQL子查询注入的邮件列表

[11 Aug 2016 14:36] Shahriyar Rzayev

Description:
Running query is:

select  count(*), concat(version(),floor(rand(0)*2))x from information_schema.tables group by x;                    
ERROR 1062 (23000): Duplicate entry '5.7.14-labs-gr0801' for key '<group_key>'

select distinct floor(rand(0)*2) from information_schema.tables;
+------------------+
| floor(rand(0)*2) |
+------------------+
|                0 |
|                1 |
+------------------+
2 rows in set (0.01 sec)

In general the error will likely happen here:

mysql [localhost] {msandbox} (information_schema) > SELECT FLOOR(RAND(0)*2)x FROM information_schema.tables;
+---+
| x |
+---+
| 0 |
| 1 |
| 1 | <---- Duplicate entry here

select count(*), concat(version(),floor(rand(0)*2)) from information_schema.tables group by concat(2,floor(rand(0)*2));
ERROR 1062 (23000): Duplicate entry '21' for key '<group_key>'

Another variation here:

mysql [localhost] {msandbox} (information_schema) > select 'f', concat(version(),floor(rand(0)*2)) from information_schema.tables group by concat(2,floor(rand(0)*2));
+---+------------------------------------+
| f | concat(version(),floor(rand(0)*2)) |
+---+------------------------------------+
| f | 5.7.14-labs-gr0800                 |
| f | 5.7.14-labs-gr0801                 |
+---+------------------------------------+
2 rows in set (0.00 sec)

So it will happen while using aggregation. Question is -> why? :)

How to repeat:
See description

[11 Aug 2016 14:37] Shahriyar Rzayev

Changed category.

[11 Aug 2016 15:38] Sinisa Milivojevic

Hi!

You are using rand() in both a select list and in the group list. That can create huge runtime problems. How does this work:

select count(*), concat(version(),floor(rand(0)*2)),  concat(2,floor(rand(0)*2))  as xxx from
information_schema.tables group by xxx;

[15 Aug 2016 9:58] Shahriyar Rzayev

Hi,
The result is:

mysql [localhost] {msandbox} ((none)) > select count(*), concat(version(),floor(rand(0)*2)),  concat(2,floor(rand(0)*2))  as xxx from information_schema.tables group by xxx;
ERROR 1062 (23000): Duplicate entry '21' for key '<group_key>'

[16 Aug 2016 14:28] Sinisa Milivojevic

Hi,

You are quite right. rand() can not be used in GROUP BY reliably. Hence, we need to document it properly.

Thanks.

[17 Aug 2016 14:57] Paul Dubois

http://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html#function_rand says:

Use of a column with RAND() values in an ORDER BY or GROUP BY clause may yield unexpected results because for either clause a RAND() expression can be evaluated multiple times for the same row, each time returning a different result. 

What you are seeing is one manifestation of "unexpected results."