mysql数据库groupby报错原理是什么？

八一xiaobayi

2020-03-18 09:05:04

mysql> select count(9),floor(rand(0)*2) as a from information_schema.tables group by a order by null;ERROR 1062 (23000): Duplicate entry '1' for key 'group_key'mysql>上面这句话的先后顺序是什么？是先order by 还是group by 还是count(9) ？mysql> select count(9),floor(rand(0)*2) as a from information_schema.tables group by a order by null;ERROR 1062 (23000): Duplicate entry '1' for key 'group_key'mysql> select count(9),floor(rand(0)*2) as a from mysql.user group by a order by null;+----------+---+| count(9) | a |+----------+---+| 2 | 1 |+----------+---+1 row in set (0.00 sec)mysql> grant all on *.* to root@'192.%' identified by '123456';Query OK, 0 rows affected (0.01 sec)mysql> select host,user,password from mysql.user;+-------------+------+-------------------------------------------+| host | user | password |+-------------+------+-------------------------------------------+| 127.% | root | *81F5E21E35407D884A6CD4A731AEBFB6AF209E1B || 127.0.0.1 | root | *81F5E21E35407D884A6CD4A731AEBFB6AF209E1B || 192.% | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 || 192.168.% | root | *23AE809DDACAF96AF0FD78ED04B6A265E05AA257 || 192.168.0.% | root | *A4B6157319038724E3560894F7F932C8886EBFCF |+-------------+------+-------------------------------------------+5 rows in set (0.00 sec)mysql> select count(9),floor(rand(0)*4) as a from mysql.user group by a order by null;ERROR 1062 (23000): Duplicate entry '2' for key 'group_key'为什么mysql.user记录大于3,才报错

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