jorgecarleitao commented on a change in pull request #9776:
URL: https://github.com/apache/arrow/pull/9776#discussion_r599994379



##########
File path: rust/datafusion/tests/sql.rs
##########
@@ -1940,6 +1940,56 @@ async fn query_without_from() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn query_cte() -> Result<()> {
+    // Test for SELECT <expression> without FROM.
+    // Should evaluate expressions in project position.
+    let mut ctx = ExecutionContext::new();
+
+    // simple with
+    let sql = "WITH t AS (SELECT 1) SELECT * FROM t";
+    let actual = execute(&mut ctx, sql).await;
+    let expected = vec![vec!["1"]];
+    assert_eq!(expected, actual);
+
+    // with + union
+    let sql = "WITH t AS (SELECT 1 AS a), u AS (SELECT 2 AS a) SELECT * FROM t 
UNION ALL SELECT * FROM u";
+    let actual = execute(&mut ctx, sql).await;
+    let expected = vec![vec!["1"], vec!["2"]];
+    assert_eq!(expected, actual);
+
+    // with + join
+    let sql = "WITH t AS (SELECT 1 AS id1), u AS (SELECT 1 AS id2, 5 as x) 
SELECT x FROM t JOIN u ON (id1 = id2)";
+    let actual = execute(&mut ctx, sql).await;
+    let expected = vec![vec!["5"]];
+    assert_eq!(expected, actual);
+
+    // backward reference
+    let sql = "WITH t AS (SELECT 1 AS id1), u AS (SELECT * FROM t) SELECT * 
from u";
+    let actual = execute(&mut ctx, sql).await;
+    let expected = vec![vec!["1"]];
+    assert_eq!(expected, actual);
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn query_cte_incorrect() -> Result<()> {
+    let ctx = ExecutionContext::new();
+
+    // self reference
+    let sql = "WITH t AS (SELECT * FROM t) SELECT * from u";
+    let plan = ctx.create_logical_plan(&sql);
+    assert!(plan.is_err());
+
+    // forward referencing
+    let sql = "WITH t AS (SELECT * FROM u), u AS (SELECT 1) SELECT * from u";
+    let plan = ctx.create_logical_plan(&sql);
+    assert!(plan.is_err());

Review comment:
       Out of curiosity, what is the error message here? Is it worth asserting 
about its content?




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