alamb commented on code in PR #8629:
URL: https://github.com/apache/arrow-datafusion/pull/8629#discussion_r1435239529
##########
datafusion/expr/src/logical_plan/builder.rs:
##########
@@ -1189,6 +1173,42 @@ pub fn build_join_schema(
schema.with_functional_dependencies(func_dependencies)
}
+/// Add additional "synthetic" group by expressions based on functional
+/// dependencies.
+///
+/// For example, if we are grouping on `[c1]`, and we know from
+/// functional dependencies that column `c1` determines `c2`, this function
+/// adds `c2` to the group by list.
+///
+/// This allows MySQL style selects like
+/// `SELECT col FROM t WHERE pk = 5` if col is unique
+fn add_group_by_exprs_from_dependencies(
Review Comment:
I pulled the logic into its own function so I could document it better
##########
datafusion/expr/src/logical_plan/builder.rs:
##########
@@ -1189,6 +1173,42 @@ pub fn build_join_schema(
schema.with_functional_dependencies(func_dependencies)
}
+/// Add additional "synthetic" group by expressions based on functional
+/// dependencies.
+///
+/// For example, if we are grouping on `[c1]`, and we know from
+/// functional dependencies that column `c1` determines `c2`, this function
+/// adds `c2` to the group by list.
+///
+/// This allows MySQL style selects like
+/// `SELECT col FROM t WHERE pk = 5` if col is unique
+fn add_group_by_exprs_from_dependencies(
+ mut group_expr: Vec<Expr>,
+ schema: &DFSchemaRef,
+) -> Result<Vec<Expr>> {
+ // Names of the fields produced by the GROUP BY exprs for example, `GROUP
BY
+ // c1 + 1` produces an output field named `"c1 + 1"`
+ let mut group_by_field_names = group_expr
+ .iter()
+ .map(|e| e.display_name())
+ .collect::<Result<Vec<_>>>()?;
+
+ if let Some(target_indices) =
+ get_target_functional_dependencies(schema, &group_by_field_names)
+ {
+ for idx in target_indices {
+ let field = schema.field(idx);
+ let expr =
+ Expr::Column(Column::new(field.qualifier().cloned(),
field.name()));
+ let expr_name = expr.display_name()?;
+ if !group_by_field_names.contains(&expr_name) {
Review Comment:
this is the change -- rather than comparing the `Expr`s it compares their
`display_name` (the fields they will create)
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