alamb commented on code in PR #14699: URL: https://github.com/apache/datafusion/pull/14699#discussion_r1966502387
########## datafusion/physical-expr-common/src/physical_expr.rs: ########## @@ -144,6 +153,111 @@ pub trait PhysicalExpr: Send + Sync + Display + Debug + DynEq + DynHash { Ok(Some(vec![])) } + /// Computes the output statistics for the expression, given the input + /// statistics. + /// + /// # Parameters + /// + /// * `children` are the statistics for the children (inputs) of this + /// expression. + /// + /// # Returns + /// + /// A `Result` containing the output statistics for the expression in + /// case of success, or an error object in case of failure. + /// + /// Expressions (should) implement this function and utilize the independence + /// assumption, match on children distribution types and compute the output + /// statistics accordingly. The default implementation simply creates an + /// unknown output distribution by combining input ranges. This logic loses + /// distribution information, but is a safe default. + fn evaluate_statistics(&self, children: &[&StatisticsV2]) -> Result<StatisticsV2> { Review Comment: I did some more research into the current code, which has: 1. [`Statistics`](https://docs.rs/datafusion/latest/datafusion/common/struct.Statistics.html) has table level statistics, such as statistics for columns and the row count and distinct count 2. [`ColumnStatistics`](https://docs.rs/datafusion/latest/datafusion/common/struct.ColumnStatistics.html) which has column level statistics In this PR 1. `[&StatisticsV2]` is equivalent to `Statistics` ( distribution of multiple columns) 2. `StatisticsV2` is equivalent to `ColumnStatistics` (distribution of a single column) In order to have the names be consistent, I recommend: 1. Renaming `StatisticsV2` to `ColumnStatisticsV2` 2. Introducing `StatisticsV2` that holds a set of column statistics -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: github-unsubscr...@datafusion.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: github-unsubscr...@datafusion.apache.org For additional commands, e-mail: github-h...@datafusion.apache.org