The current join estimation logic is only based on basic column statistics (such as ndv, etc). If we want to add estimation for other kinds of statistics (such as histograms), it's not easy to incorporate into the current algorithm:
1. When we have multiple pairs of join keys, the current algorithm computes cardinality in a single formula. But if different join keys have different kinds of stats, the computation logic for each pair of join keys become different, so the previous formula does not apply.
2. Currently it computes cardinality and updates join keys' column stats separately. It's better to do these two steps together, since both computation and update logic are different for different kinds of stats.