yjshen opened a new issue #2064:
URL: https://github.com/apache/arrow-datafusion/issues/2064
`CASE WHEN a > 0 THEN 25.0 / cast(a, float64) ELSE float64(null) END` will
fail with error: `ArrowError(DivideByZero)`, since we are computing `25 div a`
without checking the `when` condition.
To reproduce
```rust
#[test]
fn case_without_expr1() -> Result<()> {
let batch = case_test_batch1()?;
let schema = batch.schema();
// CASE WHEN a > 0 THEN 25.0 / cast(a, float64) ELSE float64(null)
END
let when1 = binary(
col("a", &schema)?,
Operator::Gt,
lit(ScalarValue::Int32(Some(0))),
&batch.schema(),
)?;
let then1 = binary(
lit(ScalarValue::Float64(Some(25.0))),
Operator::Divide,
cast(col("a", &schema)?, &batch.schema(), Float64)?,
&batch.schema(),
)?;
let x = lit(ScalarValue::Float64(None));
let expr = case(None, &[(when1, then1)], Some(x))?;
let result = expr.evaluate(&batch)?.into_array(batch.num_rows());
let result = result
.as_any()
.downcast_ref::<Float64Array>()
.expect("failed to downcast to Int32Array");
let expected = &Float64Array::from(vec![Some(25.0), None, None,
Some(5.0)]);
assert_eq!(expected, result);
Ok(())
}
fn case_test_batch1() -> Result<RecordBatch> {
let schema = Schema::new(vec![Field::new("a", DataType::Int32,
true)]);
let a = Int32Array::from(vec![Some(1), Some(0), None, Some(5)]);
let batch = RecordBatch::try_new(Arc::new(schema),
vec![Arc::new(a)])?;
Ok(batch)
}
```
The
[cause](https://github.com/apache/arrow-datafusion/blob/master/datafusion-physical-expr/src/expressions/case.rs#L344)
of the problem:
```rust
for i in (0..self.when_then_expr.len()).rev() {
let i = i as usize;
let when_value = self.when_then_expr[i].0.evaluate(batch)?;
let when_value = when_value.into_array(batch.num_rows());
let then_value = self.when_then_expr[i].1.evaluate(batch)?;
// <------------
let then_value = then_value.into_array(batch.num_rows());
```
We are not checking the "selection vector" generated by the `when clause` to
evaluate `then clause`.
A possible solution with minimum changes from arrow kernel computations
might be:
```rust
pub trait PhysicalExpr: Send + Sync + Display + Debug {
......
.....
/// Evaluate an expression against a RecordBatch with validity array
fn evaluate_selection(&self, batch: &RecordBatch, selection:
BooleanArray) -> Result<ColumnarValue> {
let valid_batch = take_all_valid(batch, &selection);
let tmp = self.evaluate(&valid_batch)?;
Ok(scatter(tmp, &selection))
}
}
```
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