Support decimal for sql execution.

[nett32]

Description

Please explain the changes you made here.

Checklist

• Code compiles correctly
• Created tests which fail without the change (if possible)
• All tests passing
• Extended the README / documentation, if necessary
• Added myself / the copyright holder to the AUTHORS file

[methane]

I don't like it. It doesn't true decimal support.
It is just pass the string without escaping or quoting.
Essencially, it is same to fmt.Sprintf, but far complicated and poor performance.

[nett32]

@methane I updated the code implementation.

[methane]

It doesn't make sense at all.