Why Cast Decimal gives incorrect result in CnosDB?

Question

I ran the followed SQL:

select cast(6.4053151420411946063694043751862251568 as decimal(38,37));

It returned:

+-----------------------------------------+
| Float64(6.405315142041195)              |
+-----------------------------------------+
| 6.4053151420411954619510965656866521088 |
+-----------------------------------------+

But it should return 6.4053151420411946063694043751862251568.

How to get the correct result?