jiangzhx commented on issue #5791:
URL:
https://github.com/apache/arrow-datafusion/issues/5791#issuecomment-1502692953
i find a way to create scalar subquery when use dataframe.
There are 3 places here that need attention in order to write the correct
code.
1. `.select(vec![count(lit(COUNT_STAR_EXPANSION))])? ` should add after
aggregate, scalar_subquery_to_join look like need this
3. `count(*)` rewrite to `count(lit(COUNT_STAR_EXPANSION))` after #5686
merge ,it's not necessary.
4. ` .into_optimized_plan()` rewrite to `.into_unoptimized_plan()` because
eliminate_projection will remove this. then got scalar_subquery_to_join not work
Maybe it's just me, but writing the correct code using a dataframe is not
easy. We should write a document for this place.
the right way to create scalar subquery with dataframe api.
```
#[tokio::test]
async fn test_count_wildcard_on_where_scalar_subquery() -> Result<()> {
let ctx = create_join_context()?;
ctx.sql("select a,b from t1 where (select count(*) from t2 where t1.a =
t2.a)>0;")
.await?
.explain(false, false)?
.show()
.await?;
let subquery = Expr::ScalarSubquery(datafusion_expr::Subquery {
subquery: Arc::new(
ctx.table("t2")
.await?
.filter(col("t1.a").eq(col("t2.a")))?
.aggregate(vec![], vec![count(lit(COUNT_STAR_EXPANSION))])?
.select(vec![count(lit(COUNT_STAR_EXPANSION))])?
.into_unoptimized_plan(),
),
outer_ref_columns: vec![],
});
ctx.table("t1")
.await?
.filter(subquery.gt(lit(ScalarValue::UInt8(Some(0)))))?
.select(vec![col("t1.a"), col("t1.b")])?
.explain(false, false)?
.show()
.await?;
Ok(())
}
```
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