bersprockets opened a new pull request, #41353:
URL: https://github.com/apache/spark/pull/41353
### What changes were proposed in this pull request?
In `StringUtils#orderSuggestedIdentifiersBySimilarity`, handle the case
where the candidate attributes have a mix of empty and non-empty prefixes.
### Why are the changes needed?
The following query throws a `StringIndexOutOfBoundsException`:
```
with v1 as (
select * from values (1, 2) as (c1, c2)
),
v2 as (
select * from values (2, 3) as (c1, c2)
)
select v1.c1, v1.c2, v2.c1, v2.c2, b
from v1
full outer join v2
using (c1);
```
The query should fail anyway, since `b` refers to a non-existent column. But
it should fail with a helpful error message, not with a
`StringIndexOutOfBoundsException`.
`StringUtils#orderSuggestedIdentifiersBySimilarity` assumes that a list of
suggested attributes with a mix of prefixes will never have an attribute name
with an empty prefix. But in this case it does (`c1` from the `coalesce` has no
prefix, since it is not associated with any relation or subquery):
```
+- 'Project [c1#5, c2#6, c1#7, c2#8, 'b]
+- Project [coalesce(c1#5, c1#7) AS c1#9, c2#6, c2#8] <== c1#9 has no
prefix, unlike c2#6 (v1.c2) or c2#8 (v2.c2)
+- Join FullOuter, (c1#5 = c1#7)
:- SubqueryAlias v1
: +- CTERelationRef 0, true, [c1#5, c2#6]
+- SubqueryAlias v2
+- CTERelationRef 1, true, [c1#7, c2#8]
```
Because of this, `orderSuggestedIdentifiersBySimilarity` returns a sorted
list of suggestions like this:
```
ArrayBuffer(.c1, v1.c2, v2.c2)
```
`UnresolvedAttribute.parseAttributeName` chokes on an attribute name that
starts with a '.'.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
New unit tests.
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