morrySnow commented on code in PR #14730:
URL: https://github.com/apache/doris/pull/14730#discussion_r1037973927
##########
fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/algebra/Project.java:
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@@ -55,4 +58,79 @@ default Map<Slot, Expression> getAliasToProducer() {
)
);
}
+
+ /**
+ * combine upper level and bottom level projections
+ * 1. alias combination, for example
+ * proj(x as y, b) --> proj(a as x, b, c) =>(a as y, b)
+ * 2. remove used projection in bottom project
+ * @param childProject bottom project
+ * @return project list for merged project
+ */
+ default List<NamedExpression> mergeProjections(Project childProject) {
Review Comment:
nit: maybe a static function is better
```sql
List<NamedExpression> mergeProjections(List<NamedExpression> top,
List<NamedExpression> bottom)
```
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