alamb commented on code in PR #2142:
URL: https://github.com/apache/arrow-datafusion/pull/2142#discussion_r845526998
##########
datafusion/physical-expr/src/expressions/binary.rs:
##########
@@ -485,22 +485,31 @@ fn bitwise_or(left: ArrayRef, right: ArrayRef) ->
Result<ArrayRef> {
}
}
-/// Use datafusion build-in expression `concat` to evaluate `StringConcat`
operator
+/// Use datafusion build-in expression `concat` to evaluate `StringConcat`
operator.
+/// Besides, any `NULL` exists on lhs or rhs will come out result `NULL`
+/// 1. 'a' || 'b' || 32 = 'ab32'
+/// 2. 'a' || NULL = NULL
fn string_concat(left: ArrayRef, right: ArrayRef) -> Result<ArrayRef> {
- // return NULL if left or right is NULL
- for i in 0..left.len() {
- if left.is_null(i) || right.is_null(i) {
- return Ok(new_null_array(&DataType::Utf8, left.len()));
- }
- }
- let result = string_expressions::concat(&[
- ColumnarValue::Array(left),
- ColumnarValue::Array(right),
- ])?;
- match result {
- ColumnarValue::Array(array_ref) => Ok(array_ref),
- scalar_value => Ok(scalar_value.into_array(1)),
- }
+ let ignore_null = match string_expressions::concat(&[
+ ColumnarValue::Array(left.clone()),
+ ColumnarValue::Array(right.clone()),
+ ])? {
+ ColumnarValue::Array(array_ref) => array_ref,
+ scalar_value => scalar_value.into_array(left.clone().len()),
+ };
+ let ignore_null_array =
ignore_null.as_any().downcast_ref::<StringArray>().unwrap();
+ let result = (0..ignore_null_array.len())
+ .into_iter()
+ .map(|index| {
+ if left.is_null(index) || right.is_null(index) {
+ None
+ } else {
+ Some(ignore_null_array.value(index))
+ }
+ })
+ .collect::<StringArray>();
Review Comment:
As a future optimization it might be worth using the `take` kernel
https://docs.rs/arrow/11.1.0/arrow/compute/kernels/take/fn.take.html which is
fairly well optimized / tries to avoid copying.
This is good for now though
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