xitep opened a new pull request, #2235:
URL: https://github.com/apache/datafusion-sqlparser-rs/pull/2235
* `SetExpr` is a directly recursive data-structure through
`SetExpr::SetOperation`
* Its visit impl dispatches directly to `Select` (without necessary going
through `Query` first)
* Right now a `Visitor` impl has no chance to observe the scope of a visited
SELECT
The motivation is that `SELECT`s often introduce aliases which are valid
only for that particular SELECT.
```sql
select *
from (select 1 val from dual) x
where x.val = 1
union all
select *
from (select 2 val from dual) y
where y.val = 2
-- referring to `x` at this point is an error
```
This change allows effectively to determine the scope of a (nested) SELECT
using `Visitor/Mut`.
Alternatively we could entirely drop `SetExpr::Select` and replace it's use
with `SetExpr::Query`; after all a `Select` is a Query's body. (My personal
preference would be to keep the current structure as it makes the AST easier to
follow / navigate / more expressive.)
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