[GitHub] [arrow-datafusion] renato2099 commented on a diff in pull request #2142: implement 'StringConcat' operator to support sql like "select 'aa' || 'b' "

[GitBox <gi...@apache.org>]

renato2099 commented on code in PR #2142:
URL: https://github.com/apache/arrow-datafusion/pull/2142#discussion_r841282224


##########
datafusion/core/tests/sql/expr.rs:
##########
@@ -280,6 +280,47 @@ async fn query_scalar_minus_array() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn test_string_concat_operator() -> Result<()> {
+    let ctx = SessionContext::new();
+    // concat 2 strings
+    let sql = "SELECT 'aa' || 'b'";
+    let actual = execute_to_batches(&ctx, sql).await;
+    let expected = vec![
+        "+-------------------------+",
+        "| Utf8(\"aa\") || Utf8(\"b\") |",
+        "+-------------------------+",
+        "| aab                     |",
+        "+-------------------------+",
+    ];
+    assert_batches_eq!(expected, &actual);
+
+    // concat 4 strings as a string concat pipe.
+    let sql = "SELECT 'aa' || 'b' || 'cc' || 'd'";
+    let expected = vec![
+        "+----------------------------------------------------+",
+        "| Utf8(\"aa\") || Utf8(\"b\") || Utf8(\"cc\") || Utf8(\"d\") |",
+        "+----------------------------------------------------+",
+        "| aabccd                                             |",
+        "+----------------------------------------------------+",
+    ];
+    let actual = execute_to_batches(&ctx, sql).await;
+    assert_batches_eq!(expected, &actual);
+
+    // concat 3 strings with one is NULL
+    let sql = "SELECT 'aa' || NULL || 'd'";
+    let expected = vec![

Review Comment:
   as a user I would also expect that any operation involving  a `null` value would actually return `null` since `null != empty`, maybe there is a SQL spec somewhere we could check?



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