Question

Why there is not possible to ask related question to question, only to answers ?

Answer 1

This was a deliberate design decision. I think it's pretty rare for a question to trigger another one, without an answer between. But I'm open to your comments...

Comments

I think the way you did it is fine, although personally I turned it off because I'm not really sure of the benefit of a question being related to another. I thought you may as well just click the regular ask question button.

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My intuition was that questions would be related to other questions, not related to answers.  Whether or not I am in the majority there I don't know, but the "Ask a related question" text does get awfully repetitive for questions that have lots of answers.

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I find users do often ask related questions as comments to answers, follow up questions to detailed answers, mainly.  This threatens to clog up the forum, so that's when I point out the Related Question button.  For me it works great, and I would never have thought of implementing it myself (kudos!).  

I wouldn't be too interested in a related to the question button, though, since it's pretty obvious what to do if you have a similar question, and people don't seem to post such questions as answers or comments.

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@NoahY - thanks for the reply.  Good to know.  Btw, can you link to your implementation of this project?  I'd love to check it out.

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I created an internal bug tracking system long ago that had the notion of stapling tickets together.  

This would be used in the case of two similar but distinct tickets that should be tracked or resolved together (ie, both dealing with the same problem or enhancement) or when they were duplicates (you might close one but add a reference from it to the ticket that was kept live).

I get the ask a related question process and I agree with @Gidgreen but I also see the benefit of a separate process of linking two questions together.  We see this all the time on Stack Overflow - its a manual process where someone will past a link into the comments to denote the linkage - this isn't a good solution for obvious reasons.

I'd like to see the ability to link already existing questions to other posts (questions or answers).  I posted a question related to this (but can't link it since there's no way to do that presently, sorry for the URL linkage) - http://www.question2answer.org/qa/15639/there-way-relate-one-question-another-when-both-already-exist