nuno-faria opened a new issue, #15688:
URL: https://github.com/apache/datafusion/issues/15688
### Describe the bug
The unparse of Join operators is ignoring the projected columns, ending up
projecting everything.
Two conditions cause this to happen:
- the final projected columns match the columns in the `TableScans`, meaning
the `Projection` is optimized away with the `optimize_projections` rule;
- the `try_transform_to_simple_table_scan_with_filters` function in the
`unparser` module -- used when processing joins -- causes the `TableScan`
projection to be discarded.
I could try to fix this by modifying the join unparser, but I would like to
be sure that this is the best approach here.
### To Reproduce
```rust
use datafusion::error::Result;
use datafusion::prelude::SessionContext;
use datafusion::sql::unparser::Unparser;
use datafusion::sql::unparser::dialect::PostgreSqlDialect;
#[tokio::main]
async fn main() -> Result<()> {
let ctx = SessionContext::new();
ctx.sql("create table test (k int, v int)")
.await?
.collect()
.await?;
let df = ctx.sql("select t1.v, t2.v from test t1, test t2").await?;
println!("{}\n", df.logical_plan());
let plan = df.into_optimized_plan()?;
println!("{}\n", plan);
println!(
"{}",
Unparser::new(&PostgreSqlDialect {})
.plan_to_sql(&plan)
.unwrap()
);
Ok(())
}
```
```
Projection: t1.v, t2.v
Cross Join:
SubqueryAlias: t1
TableScan: test
SubqueryAlias: t2
TableScan: test
Cross Join:
SubqueryAlias: t1
TableScan: test projection=[v]
SubqueryAlias: t2
TableScan: test projection=[v]
SELECT * FROM "test" AS "t1" CROSS JOIN "test" AS "t2"
```
### Expected behavior
Output the query with the projected fields:
```
SELECT "t1".v, "t2".v FROM "test" AS "t1" CROSS JOIN "test" AS "t2"
```
### Additional context
_No response_
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