Dandandan commented on a change in pull request #519:
URL: https://github.com/apache/arrow-datafusion/pull/519#discussion_r646165300
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File path: datafusion/src/sql/utils.rs
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@@ -390,6 +390,42 @@ pub(crate) fn extract_aliases(exprs: &[Expr]) ->
HashMap<String, Expr> {
.collect::<HashMap<String, Expr>>()
}
+/// Returns mapping of each position (`String`) to the expression (`Expr`) it
is
+/// aliasing.
+pub(crate) fn extract_positions(exprs: &[Expr]) -> HashMap<String, Expr> {
+ let mut position = 0;
+ exprs
+ .iter()
+ .filter_map(|expr| match expr {
+ // position starts with 1
+ Expr::Alias(nested_expr, _alias_name) => {
+ position += 1;
+ Some((position.clone().to_string(), *nested_expr.clone()))
+ }
+ _ => {
+ position += 1;
+ Some((position.clone().to_string(), expr.clone()))
+ }
+ })
+ .collect::<HashMap<String, Expr>>()
+}
+
+pub(crate) fn resolve_positions_to_exprs(
+ expr: &Expr,
+ positions: &HashMap<String, Expr>,
+) -> Result<Expr> {
Review comment:
If we pass the `exprs: &[Expr]` to this function we can index to it
directly by `i - 1`.
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