comphead commented on issue #1681:
URL:
https://github.com/apache/datafusion-comet/issues/1681#issuecomment-2830857856
> > > interesting that referring to first column which is `a` returns result
correctly, but `b` does not
> >
> >
> > This is because we read all fields in the struct, so we are guaranteed
to produce the correct results in the following cases:
> > ```
> > * the user only selects the first field
> >
> > * the user selects all fields
> > ```
>
> That is not quite correct. We will accidentally have the correct behavior
when the user selects a set of fields starting with the first field and not
skipping any fields in that range. So for a struct with fields `a, b, c, d`, we
will have correct behavior for reading `a` or `a, b` or `a, b, c`, or `a, b, c,
d`.
Reverse also works. but `a, c` skipping `b` doesn't
```
PASSED
test("native reader - read a STRUCT subfield from ARRAY of STRUCTS - field
from first") {
testSingleLineQuery(
"""
| select array(str0, str1) c0 from
| (
| select
| named_struct('a', 1, 'b', 'n', 'c', 'x') str0,
| named_struct('a', 2, 'b', 'w', 'c', 'y') str1
| )
|""".stripMargin,
"select c0[0].a, c0[0].b, c0[0].c from tbl")
}
PASSED
test("native reader - read a STRUCT subfield from ARRAY of STRUCTS -
reverse fields") {
testSingleLineQuery(
"""
| select array(str0, str1) c0 from
| (
| select
| named_struct('a', 1, 'b', 'n', 'c', 'x') str0,
| named_struct('a', 2, 'b', 'w', 'c', 'y') str1
| )
|""".stripMargin,
"select c0[0].c, c0[0].b, c0[0].a from tbl")
}
FAILED
test("native reader - read a STRUCT subfield from ARRAY of STRUCTS - skip
field") {
testSingleLineQuery(
"""
| select array(str0, str1) c0 from
| (
| select
| named_struct('a', 1, 'b', 'n', 'c', 'x') str0,
| named_struct('a', 2, 'b', 'w', 'c', 'y') str1
| )
|""".stripMargin,
"select c0[0].a, c0[0].c from tbl")
}
```
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