You might like to look at this for comma use: Using Commas
The books I have refered on punctuations mention that if the phrase with a subordinating adverbial conjunctions (e.g. although) comes first then a comma is required and no comma otherwise.
What about adjective conjunctions. I have seen sentences which contain commas even when these come at the end of main clause
They say he is honest, which is far from truth
I dont think I got an answer to my question. The link talks about adverbial conjunction, not much about adjective conjunctions. However, it talks about adjective conjunctions only in the context of setting of clauses within main clause ...
In the sentence you quote it introduces a relative clause which refers to the whole of the previous clause (They say he is honest) and which is called a sentence relative. As such, yes, it must come after the main clause and should be preceded by a comma.
I agree that my question was incorrect.
Let me rephrase it again.
My question was regarding relative adjectives e.g. which that what whichever
When these clauses follow main clause, is there a need for comma punctuation.
that, what and whichever are not.
These are things that are in discussion
There is no saying what he will do
The driver took whichever road to the right he could.