[[feature collection]] requested Functions and query operators

This issue contains a list of related feature requests that are not on the near-term roadmap. The feature requests in this issue are all new functions that have been requested. If you want to request a function not already listed please make a comment on this issue, and we will add it to the checklist.
#### Aggregations
- [x] moving averages function: https://github.com/influxdata/influxdb/issues/77
- [ ] histogram https://github.com/influxdata/influxdb/issues/3674
- [x] cumulative counts https://github.com/influxdata/influxdb/issues/813
- [ ] HDR histogram https://github.com/influxdata/influxdb/issues/739
- [ ] histogram with log-scaled buckets https://github.com/influxdata/influxdb/issues/984
- [ ] time weighted aggregations https://github.com/influxdata/influxdb/issues/7445
- [ ] logarithmic mean https://github.com/influxdata/influxdb/issues/2482
- [x] integrals https://github.com/influxdata/influxdb/issues/1400
- [ ] cumulative distribution function: https://github.com/influxdata/influxdb/issues/7261
#### Selectors
- [ ] faster, slightly less accurate percentages calculation https://github.com/influxdata/influxdb/issues/513
- [ ] lag variables https://github.com/influxdata/influxdb/issues/142
- [ ] lead variables https://github.com/influxdata/influxdb/issues/143
- [ ] upper bound, lower bound https://github.com/influxdata/influxdb/issues/659
- [ ] average "gauges" with awareness of time spent in state https://github.com/influxdata/influxdb/issues/1115
- [x] mode https://github.com/influxdata/influxdb/issues/1823
#### Transformations
- [x] trigonometric functions (sine, cosine, etc.) https://github.com/influxdata/influxdb/issues/659
- [ ] hyperloglog https://github.com/influxdata/influxdb/issues/717
- [x] dot-product https://github.com/influxdata/influxdb/issues/5095
#### Operators
- [x] difference https://github.com/influxdata/influxdb/issues/1825
- [x] elapsed time between events https://github.com/influxdata/influxdb/issues/1856
- [x] exponents and logarithms https://github.com/influxdata/influxdb/issues/659
- [x] ceiling and floor functions https://github.com/influxdata/influxdb/issues/3691
- [ ] trend operators: linear and least square https://github.com/influxdata/influxdb/issues/5358
- [x] DIFFERENCE of two fields https://github.com/influxdata/influxdb/issues/761
#### InfluxQL enhancements
- [x] general support for nested functions https://github.com/influxdata/influxdb/issues/834
- [x] percentile + derivative https://github.com/influxdata/influxdb/issues/5150
- [ ] percentage of values above/below given value (inverse PERCENTILE)
- [x] Top accepts nested functions https://github.com/influxdata/influxdb/issues/2467, https://github.com/influxdata/influxdb/issues/5345
- [x] CAST into different data types https://github.com/influxdata/influxdb/issues/2911
- [ ] `fill(previous)` without GROUP BY https://github.com/influxdata/influxdb/issues/3633
- [ ] User defined functions https://github.com/influxdata/influxdb/issues/6891
- [ ] Boolean type cast https://github.com/influxdata/influxdb/issues/7562

This issue is a broad checklist rather than a scoped change, and it names no source files, tests, or entry points. Start by selecting one unchecked request and reviewing its linked issue; the collection itself does not define a single implementation target or completion criteria.

Written by the indexing model from the issue text.