fix: adds more information when an EXPLAIN <query> is run on a federated source

datafusion-federation/src/plan_node.rs

@@ -54,7 +54,7 @@ impl UserDefinedLogicalNodeCore for FederatedPlanNode {
     }
 
     fn fmt_for_explain(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Federated")
+        write!(f, "Federated\n {:?}", self.plan)
     }
 
     fn from_template(&self, exprs: &[Expr], inputs: &[LogicalPlan]) -> Self {

examples/examples/sqlite.rs

@@ -44,8 +44,17 @@ async fn main() -> datafusion::error::Result<()> {
          JOIN Artist ar ON a.ArtistId = ar.ArtistId
          limit 10"#;
     let df = ctx.sql(query).await?;
+    df.show().await?;
 
-    df.show().await
+    // If the environment variable EXPLAIN is set, print the query plan
+    if std::env::var("EXPLAIN").is_ok() {
+        let explain_query = format!("EXPLAIN {query}");
+        let df = ctx.sql(explain_query.as_str()).await?;
+
+        df.show().await?;
+    }
+
+    Ok(())
 }
 
 fn overwrite_default_schema(state: &SessionState, schema: Arc<dyn SchemaProvider>) -> Result<()> {

sources/sql/src/lib.rs

@@ -141,7 +141,15 @@ impl VirtualExecutionPlan {
 
 impl DisplayAs for VirtualExecutionPlan {
     fn fmt_as(&self, _t: DisplayFormatType, f: &mut fmt::Formatter) -> std::fmt::Result {
-        write!(f, "VirtualExecutionPlan")
+        write!(f, "VirtualExecutionPlan")?;
+        let Ok(ast) = plan_to_sql(&self.plan) else {
+            return Ok(());
+        };
+        write!(f, " name={}", self.executor.name())?;
+        if let Some(ctx) = self.executor.compute_context() {
+            write!(f, " compute_context={ctx}")?;
+        }
+        write!(f, " sql={ast}")
     }
 }