ARROW-8204: [Rust] [DataFusion] Add support for aliased expressions i…

…n SQL

Note that this follows on from #6703 so I'll rebase once that is merged.

Also note that this depends on sqlparser 0.2.5 which I just published.

Closes #6713 from andygrove/ARROW-8204 and squashes the following commits:

48a6a01 <Andy Grove> Add support for aliased expressions in SQL query planner

Authored-by: Andy Grove <andygrove73@gmail.com>
Signed-off-by: Paddy Horan <paddyhoran@hotmail.com>

rust/datafusion/src/sql/planner.rs

@@ -26,6 +26,7 @@ use crate::logicalplan::{
 
 use arrow::datatypes::*;
 
+use crate::logicalplan::Expr::Alias;
 use sqlparser::sqlast::*;
 
 /// The SchemaProvider trait allows the query planner to obtain meta-data about tables and
@@ -271,6 +272,10 @@ impl<S: SchemaProvider> SqlToRel<S> {
                 Ok(Expr::Literal(ScalarValue::Utf8(s.clone())))
             }
 
+            ASTNode::SQLAliasedExpr(ref expr, ref alias) => {
+                Ok(Alias(Arc::new(self.sql_to_rex(&expr, schema)?), alias.to_owned()))
+            }
+
             ASTNode::SQLIdentifier(ref id) => {
                 match schema.fields().iter().position(|c| c.name().eq(id)) {
                     Some(index) => Ok(Expr::Column(index)),
@@ -594,6 +599,14 @@ mod tests {
         quick_test(sql, expected);
     }
 
+    #[test]
+    fn select_aliased_scalar_func() {
+        let sql = "SELECT sqrt(age) AS square_people FROM person";
+        let expected = "Projection: sqrt(CAST(#3 AS Float64)) AS square_people\
+        \n  TableScan: person projection=None";
+        quick_test(sql, expected);
+    }
+
     #[test]
     fn select_order_by() {
         let sql = "SELECT id FROM person ORDER BY id";