Databases are a very poor fit for any licensing scheme, like copyleft, that is intended to encourage use by the entire world but also wants to place requirements on that use. This is because of broken legal systems and the way data is used. Projects considering copyleft, or even mere attribution, for data, should consider other approaches instead. post 
Open licensing works when you strike a healthy balance between obligations and reuse. Data, and how it is used, is different from software in ways that change that balance, making reasonable compromises in software like attribution become insanely difficult barriers.
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The right tool for building resilient, global communities of sharing is written norms, combined with a formal release of rights. Norms are essentially optimistic statements of what should be done, rather than formal requirements of what must be done. post
There is an extensive literature, pioneered by Nobelist Elinor Ostrom, on how they are actually how a huge amount of humankind’s work gets done.
Norms aren’t enough if the underlying legal system might allow an early contributor to later wield the law as a threat. That’s why the best practice in the data space is to use something like the Creative Commons public domain grant (CC-Zero) to set a clear, reliable, permissive baseline, and then use norms to add flexible requirements on top of that.