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

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

alamb commented on code in PR #2142:
URL: https://github.com/apache/arrow-datafusion/pull/2142#discussion_r842002406


##########
datafusion/physical-expr/src/expressions/binary.rs:
##########
@@ -484,6 +485,20 @@ fn bitwise_or(left: ArrayRef, right: ArrayRef) -> Result<ArrayRef> {
     }
 }
 
+/// Use datafusion build-in expression `concat` to evaluate `StringConcat` operator
+fn string_concat(left: ArrayRef, right: ArrayRef) -> Result<ArrayRef> {
+    let result = string_expressions::concat(&[
+        ColumnarValue::Array(left),
+        ColumnarValue::Array(right),
+    ])?;
+    match result {
+        ColumnarValue::Array(array_ref) => Ok(array_ref),
+        _ => Err(DataFusionError::Execution(
+            "string_concat return type should be Array, but Scalar found".to_string(),
+        )),
+    }

Review Comment:
   I think you could use `ColumnarValue::into_array` here rather than error
   
   https://github.com/apache/arrow-datafusion/blob/41b4e491663029f653e491b110d0b5e74d08a0b6/datafusion/expr/src/columnar_value.rs#L45-L50
   



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