[GitHub] [arrow-datafusion] alamb commented on a diff in pull request #2339: Add `Expr::Exists` to represent EXISTS subquery expression

[GitBox <gi...@apache.org>]

alamb commented on code in PR #2339:
URL: https://github.com/apache/arrow-datafusion/pull/2339#discussion_r858047148


##########
datafusion/expr/src/expr_fn.rs:
##########
@@ -180,6 +182,13 @@ pub fn approx_percentile_cont_with_weight(
     }
 }
 
+/// Create an EXISTS subquery expression
+pub fn exists(subquery: LogicalPlan) -> Expr {

Review Comment:
   I wonder if this function should also be added to the prelude: https://github.com/apache/arrow-datafusion/blob/b890190a6521ab1e572184dcf6ea0a5afb3a47af/datafusion/core/src/prelude.rs#L33-L40



##########
datafusion/core/src/logical_plan/builder.rs:
##########
@@ -1339,6 +1341,31 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn exists_subquery() -> Result<()> {
+        let foo = test_table_scan_with_name("foo")?;
+        let bar = test_table_scan_with_name("bar")?;
+
+        let subquery = LogicalPlanBuilder::from(foo)
+            .project(vec![col("a")])?
+            .filter(col("a").eq(col("bar.a")))?
+            .build()?;
+
+        let outer_query = LogicalPlanBuilder::from(bar)
+            .project(vec![col("a")])?
+            .filter(exists(subquery))?

Review Comment:
   👌 



##########
datafusion/core/src/physical_plan/planner.rs:
##########
@@ -186,6 +186,9 @@ fn create_physical_name(e: &Expr, is_first_expr: bool) -> Result<String> {
                 Ok(format!("{} IN ({:?})", expr, list))
             }
         }
+        Expr::Exists(_) => Err(DataFusionError::NotImplemented(
+            "EXISTS is not supported in the physical plan".to_string(),

Review Comment:
   ```suggestion
               "EXISTS is not yet supported in the physical plan".to_string(),
   ```



##########
datafusion/core/src/optimizer/utils.rs:
##########
@@ -223,6 +225,17 @@ pub fn from_plan(
             let right = &inputs[1];
             LogicalPlanBuilder::from(left).cross_join(right)?.build()
         }
+        LogicalPlan::Subquery(Subquery { .. }) => {
+            // let schema = inputs[0].schema().as_ref().clone().into();
+            // let schema =
+            //     DFSchemaRef::new(DFSchema::try_from_qualified_schema(alias, &schema)?);
+            // Ok(LogicalPlan::Subquery(Subquery {
+            //     subquery
+            //     input: Arc::new(inputs[0].clone()),
+            //     schema,
+            // }))
+            Err(DataFusionError::Plan("not implemented".to_string()))

Review Comment:
   ```suggestion
               Err(DataFusionError::Plan("subquery support is not full implemented yet".to_string()))
   ```



##########
datafusion/expr/src/expr_fn.rs:
##########
@@ -180,6 +182,13 @@ pub fn approx_percentile_cont_with_weight(
     }
 }
 
+/// Create an EXISTS subquery expression
+pub fn exists(subquery: LogicalPlan) -> Expr {

Review Comment:
   Maybe this function could take an `Arc<LogicalPlan>` so if someone already has one they can reuse it rather than making a copy to pass in here



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