如何存储(和排序)模糊的日期范围?

I have a database which needs to store year ranges (such as lifespan) which in some instances aren't very specific. For example, as well as the usual '1960', we have 'c. 1960' for "around 1960", and 1960s for in the decade 1960, as well as 'nd' for no date which is distinctly different from NULL which would be until present.I have a database which needs to store year ran