I have Stackoverflow account since 2008. I created SQA account few days ago, and afterwards linked it to same OpenId which I use for Stackoverflow. However, now I have 2 accounts listed on my profile page, with separate reputations and achievements. Only option I have is to copy my SQA profile points to stackoverflow, but I don't have options to really merge those accounts into single account. Is this by design?
Indeed it is by design.
Each site is intended to have its own reputation. The rationale for this is that the privileges in each community should be earned for that community. For example, me being a competent software developer doesn't mean I'm a very good cook. It could even do some harm: if I'm not familiar with what is accepted on a particular site, I could use reputation earned on another site inappropriately. What's the rule on software recommendations on SuperUser? Or what about this site? Are they the same? Unless you're on both sites regularly you won't really know.
Now, there are some unfortunate setbacks baked into this system. After a reasonable amount of reputation is earned on any site, one can easily spot 'close-bait' questions, and other blatant flaws that just don't fit the format of any stack exchange site. In the decisions of the powers that be, however, the setbacks are considered less significant than the risks. After all, rep is pretty easy to get, especially on small sites where people are very upvote happy :-)
Not all is lost, however. You don't start at 1 rep. If you have 200+ rep on any SE site, you will start with 101 rep on any other site. This is so you can do most of the basics (upvote, comment, etc) and still have a fairly enjoyable experience. Sometimes I find it frustrating when I'm on another site and I can't, for example, make tags. That one gets me a lot. But it usually works itself out in the end.
In any case, welcome to SQA.se!