gianm commented on PR #14653:
URL: https://github.com/apache/druid/pull/14653#issuecomment-1649481881
Some tests are failing because `mv_to_array(s)` when `s` is string `null`
returns `null` array. Previously, this would get stored in frames as `[null]`,
but now it gets stored as `null`.
I am not sure if this is a good change? It seems to me that when you call
`mv_to_array(s)`, you're saying that you want to treat `s` as a multi-value
string, even if it wasn't stored that way. And multi-value string columns
cannot be `null` themselves. They can only be `[]` or `[null]`. So, IMO
`[null]` is in fact the most reasonable thing to return.
We could restore this behavior by updating `mv_to_array` to act accordingly.
For example something like this:
```
@Override
public ExprEval apply(List<Expr> args, Expr.ObjectBinding bindings)
{
final ExprEval eval = args.get(0).eval(bindings);
if (eval.type().isArray()) {
// mv_to_array always returns string array, regardless of input
array types.
return eval.castTo(ExpressionType.STRING_ARRAY);
} else {
// Return single-element array. Avoid castTo, since that returns
null array if the element is null.
return ExprEval.ofArray(ExpressionType.asArrayType(eval.type()), new
Object[]{eval.value()});
}
}
```
Thoughts?
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