All the query logic is based on assumption - data must be sorted by ActionTime.

[NLGithubWP]

In OLAP queries, such as group BY and count, we don't care about the order of records.

So such an assumption adds some inconvenience in data pre-processing for OLAP queries

[KimballCai]

Data must be sorted by ActionTime which is the hypnosis for the cohort analysis. Besides, the COOL engine focuses on cohort analysis, and we can find other methods to improve the data processing for OLAP queries,