> but I have to solve another issue with skipping/ignoring completely empty weeks.

What issue? It looks like we don't have all requirements yet. <s>

It sounds like you should determine min and max dates, then round to whatever period you use (week, months). Determine the number of days and start with REPLICATE(".",nDays). Then use STUFF() at position dDate-DMin+1 to replace the dot with character code. This would need to happen in a loop.