One additional thing to note about TDigests is that they are somewhat dependent on the order of inputs. The percentile approximations should be nearly equal for the same underlying data, especially at the extremes of the quantile range where the TDigest is inherently more accurate, they are unlikely to be identical if built in a different order. While this should have little effect on the accuracy of the estimates, it is worth noting that repeating the creation of the TDigest might have subtle differences if the call is being parallelized by Postgres. Similarly, building a TDigest by combining several subdigests using the [summary aggregate](#tdigest-summary) is likely to produce a subtley different result than combining all of the underlying data using a single [point aggregate](#tdigest).
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