Hi, Han Mingcong ~ I guess the topic you touched is the “project push down”.
One way is like Stamatis said, use the RelFieldTrimmer which belong to the sql-to-rel conversion phrase now, the default value is “false”, you can open it through the [1]. Another way is like Chunwei said, you can write rules by your self, you may need the ProjectXXXTransposeRule to transpose the project all the way down to the source(scan) node, and a rule maybe named ProjectScanRule to pass the required fields to the source. [1] https://github.com/apache/calcite/blob/f95f74a13a20413bb0074f0a3c94901a7a88305c/core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java#L5681 Best, Danny Chan 在 2019年9月12日 +0800 PM4:15，Han Mingcong <[email protected]>，写道： > Hi all, > I’m learning query optimization recently. As known, Calcite uses a volcano > optimizer which is different from other optimizers such as SparkSQL’s > Catalyst. But I’m curious how does volcano optimizer implement rules like > `ColumnPruning` in Catalyst? Or which transformation rule does Calcite use to > achieve it? > For example, we have such a SQL: > > select a from t where b > 10; > > If the schema of t is `a int, b int, c int, …`, we only need two columns ‘a’ > and ‘b’ when scan table ‘t’. > > > Mingcong Han > 2019.9.12
