for data type float, dble and mysql may get different results

[irene-coming]

dble version: 5.6.29-dble-9.9.9.9-08136d5-20181106070356

resolution: dble will not deal such case at present, and will give instruction in docs.

[sunsun314]

https://github.com/actiontech/dble-docs-cn/blob/master/3.SQL_Syntax/3.10_func_and_operators.md#3108-aggregate-group-by-functions

doc update

[irene-coming]

doc verified