fix(cubesql): Generate proper projection wrapper for duplicated members in CubeScanNode (#9233)

`CubeScanWrapperNode::generate_sql_for_node` does not handle duplicated members in `member_fields`. It results in missing realiasing projection, as it generate only one column for each member. This introduces realiasing to make those columns reappear.

`CubeScanExecutionPlan` implements this by iterating over `member_fields` while building columns, so each member in `member_fields` will get it’s own column in DF anyway.

Author: mcheshkov

packages/cubejs-testing/test/__snapshots__/smoke-cubesql.test.ts.snap

@@ -378,3 +378,13 @@ Array [
   },
 ]
 `;
+
+exports[`SQL API Postgres (Data) wrapper with duplicated members: wrapper-duplicated-members 1`] = `
+Array [
+  Object {
+    "bar": "shipped",
+    "bar_expr": "0",
+    "foo": "shipped",
+  },
+]
+`;

packages/cubejs-testing/test/smoke-cubesql.test.ts

@@ -660,5 +660,40 @@ filter_subq AS (
       const res = await connection.query(query);
       expect(res.rows).toMatchSnapshot('query-view-deep-joins');
     });
+
+    test('wrapper with duplicated members', async () => {
+      const query = `
+        SELECT
+          "foo",
+          "bar",
+          CASE
+            WHEN "bar" = 'new'
+            THEN 1
+            ELSE 0
+            END
+            AS "bar_expr"
+        FROM (
+          SELECT
+            "rows"."foo" AS "foo",
+            "rows"."bar" AS "bar"
+          FROM (
+            SELECT
+              "status" AS "foo",
+              "status" AS "bar"
+            FROM Orders
+          ) "rows"
+          GROUP BY
+            "foo",
+            "bar"
+        ) "_"
+        ORDER BY
+          "bar_expr"
+          LIMIT 1
+        ;
+      `;
+
+      const res = await connection.query(query);
+      expect(res.rows).toMatchSnapshot('wrapper-duplicated-members');
+    });
   });
 });

rust/cubesql/cubesql/src/compile/engine/df/wrapper.rs

@@ -35,7 +35,7 @@ use serde::{Deserialize, Serialize};
 use std::{
     any::Any,
     cmp::min,
-    collections::{HashMap, HashSet},
+    collections::{hash_map::Entry, HashMap, HashSet},
     convert::TryInto,
     fmt,
     future::Future,
@@ -733,6 +733,7 @@ impl CubeScanWrapperNode {
                         // And tuning literals to measures would require ugly wrapping with noop aggregation function
                         // TODO investigate Cube.js joins, try to implement dimension member expression
                         let mut has_literal_members = false;
+                        let mut has_duplicated_members = false;
                         let mut wrapper_exprs = vec![];
 
                         for (member, field) in
@@ -741,9 +742,18 @@ impl CubeScanWrapperNode {
                             let alias = remapper.add_column(&field.qualified_column())?;
                             let expr = match member {
                                 MemberField::Member(f) => {
-                                    member_to_alias.insert(f.to_string(), alias.clone());
-                                    // `alias` is column name that would be generated by Cube.js, just reference that
-                                    Expr::Column(Column::from_name(alias.clone()))
+                                    match member_to_alias.entry(f.to_string()) {
+                                        Entry::Vacant(entry) => {
+                                            entry.insert(alias.clone());
+                                            // `alias` is column name that would be generated by Cube.js, just reference that
+                                            Expr::Column(Column::from_name(alias.clone()))
+                                        }
+                                        Entry::Occupied(entry) => {
+                                            // This member already has an alias, generate wrapper that would use it
+                                            has_duplicated_members = true;
+                                            Expr::Column(Column::from_name(entry.get().clone()))
+                                        }
+                                    }
                                 }
                                 MemberField::Literal(value) => {
                                     has_literal_members = true;
@@ -770,7 +780,7 @@ impl CubeScanWrapperNode {
                             .await?;
 
                         // TODO is this check necessary?
-                        let sql = if has_literal_members {
+                        let sql = if has_literal_members || has_duplicated_members {
                             // Need to generate wrapper SELECT with literal columns
                             // Generated columns need to have same aliases as targets in `remapper`
                             // Because that's what plans higher up would use in generated SQL

rust/cubesql/cubesql/src/compile/test/test_wrapper.rs

@@ -1456,3 +1456,68 @@ WHERE
     assert_eq!(request.measures.unwrap().len(), 1);
     assert_eq!(request.dimensions.unwrap().len(), 0);
 }
+
+#[tokio::test]
+async fn wrapper_duplicated_members() {
+    if !Rewriter::sql_push_down_enabled() {
+        return;
+    }
+    init_testing_logger();
+
+    let query_plan = convert_select_to_query_plan(
+        // language=PostgreSQL
+        format!(
+            r#"
+SELECT
+    "foo",
+    "bar",
+    CASE
+        WHEN "bar" IS NOT NULL
+        THEN 1
+        ELSE 0
+        END
+    AS "bar_expr"
+FROM (
+    SELECT
+        "rows"."foo" AS "foo",
+        "rows"."bar" AS "bar"
+    FROM (
+        SELECT
+            "dim_str0" AS "foo",
+            "dim_str0" AS "bar"
+        FROM MultiTypeCube
+    ) "rows"
+    GROUP BY
+        "foo",
+        "bar"
+) "_"
+ORDER BY
+    "bar_expr"
+LIMIT 1
+;
+        "#
+        )
+        .to_string(),
+        DatabaseProtocol::PostgreSQL,
+    )
+    .await;
+
+    let physical_plan = query_plan.as_physical_plan().await.unwrap();
+    println!(
+        "Physical plan: {}",
+        displayable(physical_plan.as_ref()).indent()
+    );
+
+    let logical_plan = query_plan.as_logical_plan();
+    // Generated SQL should contain realiasing of one member to two columns
+    assert!(logical_plan
+        .find_cube_scan_wrapped_sql()
+        .wrapped_sql
+        .sql
+        .contains(r#""foo" "foo""#));
+    assert!(logical_plan
+        .find_cube_scan_wrapped_sql()
+        .wrapped_sql
+        .sql
+        .contains(r#""foo" "bar""#));
+}