Why dulpicate error is shown in less-5 and 6, without any duplicate data's

[rahul-sani]

I just have completed the video 6 , I'm getting all the outputsl as expected. But I'm not understanding why it is throwing that error.

ie : ERROR 1062 (23000): Duplicate entry 'security::1' for key '<group_key>'

mysql> select count(*), concat((select database()),0x3a,0x3a,floor(rand()2))dump from information_schema.columns group by dump;
+----------+-------------+
| count() | dump |
+----------+-------------+
| 1501 | security::0 |
| 1603 | security::1 |
+----------+-------------+
2 rows in set (0.04 sec)

mysql> select count(*), concat((select database()),0x3a,0x3a,floor(rand()*2))dump from information_schema.columns group by dump;
ERROR 1062 (23000): Duplicate entry 'security::1' for key '<group_key>'

My doubt is there is no duplication of data right? security:: 0 's count is 1501 while the count of security::1 is 1603

So why is this error coming.