LiaCastaneda commented on issue #17508:
URL: https://github.com/apache/datafusion/issues/17508#issuecomment-3575072353
Sorry I think I misunderstood the issue, I graphed this to better picture
this, please let me know if I'm understanding this wrong
`SELECT B.C, CAST(B.C as TEXT) FROM table;
` yields to the following structure
```
╔═══════════════════╦══════════════╦══════════════╦═══════════════╗
║ Expression ║ Qualifier ║ qualified_ ║ schema_name() ║
║ ║ .0 ║ name().1 ║ ║
╠═══════════════════╬══════════════╬══════════════╬═══════════════╣
║ Column(B.C) ║ Some("B") ║ "C" ║ "B.C" ║
║ ║ ↑ ║ ↑ ║ ↑ ║
║ ║ Has table! ║ Field only ║ Combined ║
╠═══════════════════╬══════════════╬══════════════╬═══════════════╣
║ CAST(B.C as Utf8) ║ None ║ "B.C" ║ "B.C" ║
║ ║ ↑ ║ ↑ ║ ↑ ║
║ ║ No table! ║ Full string ║ Same string ║
╚═══════════════════╩══════════════╩══════════════╩═══════════════╝
```
The null literal situation from the issue description yields to the
following structure (without the uuid workaround):
```
╔═══════════════════════════╦═══════════════╦═══════════════╦═══════════════════╗
║ Expression ║ Qualifier ║ qualified_ ║ schema_name()
║
║ ║ .0 ║ name().1 ║
(name_for_alias) ║
╠═══════════════════════════╬═══════════════╬═══════════════╬═══════════════════╣
║ lit(NULL) ║ None ║ "UTF8(NULL)" ║ "UTF8(NULL)"
║
║ (new literal in project) ║ ║ ║
║
╠═══════════════════════════╬═══════════════╬═══════════════╬═══════════════════╣
║ Column(left.UTF8(NULL)) ║ Some("left") ║ "UTF8(NULL)" ║
"left.UTF8(NULL)" ║
║ (from input after join) ║ ║ ║
║
╚═══════════════════════════╩═══════════════╩═══════════════╩═══════════════════╝
```
The solutions proposed in the issue description -> using qualified_name().1
instead of name_for_alias() to detect when to rename would directly fix the
null literal case wihtout needing to use uuids. But for the cast situation the
name tracker would never trigger a rename since it sees a different
qualified_name().1, and because the schema_name are the same they fail later in
`validate_unique_names`
iiuc we want to solve both situations while avoiding the uuid workaround.
> do we want to make it possible for two columns in the output schema to
have the same exact qualified name?
Unless I'm missing something, I don't see the harm in allowing it if
Postgres already does it.
> making CAST(B.C as Utf8) have qualified name ("B", "C") so that the name
tracker can detect column B.C has an already seen name
Do you know why right now the name tracker is not triggering a rename if
both schema names are the same? (which iiuc is what `name_for_alias` returns)
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