Support select 1

bustubx/src/execution/physical_plan/empty.rs

@@ -1,16 +1,36 @@
-use crate::catalog::{Schema, SchemaRef};
+use crate::catalog::SchemaRef;
 use crate::execution::{ExecutionContext, VolcanoExecutor};
 use crate::{BustubxResult, Tuple};
-use std::sync::Arc;
+use std::sync::atomic::{AtomicUsize, Ordering};
 
 #[derive(Debug)]
 pub struct PhysicalEmpty {
+    pub produce_row_count: usize,
     pub schema: SchemaRef,
+    outputted_count: AtomicUsize,
+}
+
+impl PhysicalEmpty {
+    pub fn new(produce_row_count: usize, schema: SchemaRef) -> Self {
+        Self {
+            produce_row_count,
+            schema,
+            outputted_count: AtomicUsize::new(0),
+        }
+    }
 }
 
 impl VolcanoExecutor for PhysicalEmpty {
-    fn next(&self, context: &mut ExecutionContext) -> BustubxResult<Option<Tuple>> {
-        Ok(None)
+    fn init(&self, _context: &mut ExecutionContext) -> BustubxResult<()> {
+        self.outputted_count.store(0, Ordering::SeqCst);
+        Ok(())
+    }
+    fn next(&self, _context: &mut ExecutionContext) -> BustubxResult<Option<Tuple>> {
+        if self.outputted_count.fetch_add(1, Ordering::SeqCst) < self.produce_row_count {
+            Ok(Some(Tuple::new(self.schema.clone(), vec![])))
+        } else {
+            Ok(None)
+        }
     }
 
     fn output_schema(&self) -> SchemaRef {

bustubx/src/expression/literal.rs

@@ -4,7 +4,6 @@ use crate::common::ScalarValue;
 use crate::error::BustubxResult;
 use crate::expression::ExprTrait;
 use crate::storage::Tuple;
-use crate::BustubxError;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Literal {
@@ -24,10 +23,10 @@ impl ExprTrait for Literal {
         Ok(self.value.clone())
     }
 
-    fn to_column(&self, _input_schema: &Schema) -> BustubxResult<Column> {
-        Err(BustubxError::Plan(format!(
-            "expr {:?} as column not supported",
-            self
-        )))
+    fn to_column(&self, input_schema: &Schema) -> BustubxResult<Column> {
+        Ok(Column::new(
+            format!("{}", self.value),
+            self.data_type(input_schema)?,
+        ))
     }
 }

bustubx/src/planner/physical_planner/physical_planner.rs

@@ -135,9 +135,10 @@ pub fn build_plan(logical_plan: Arc<LogicalPlan>) -> PhysicalPlan {
         LogicalPlan::EmptyRelation(EmptyRelation {
             produce_one_row,
             schema,
-        }) => PhysicalPlan::Empty(PhysicalEmpty {
-            schema: schema.clone(),
-        }),
+        }) => PhysicalPlan::Empty(PhysicalEmpty::new(
+            if *produce_one_row { 1 } else { 0 },
+            schema.clone(),
+        )),
     };
     plan
 }

tests/sqllogictest/slt/select.slt

@@ -9,4 +9,9 @@ select a, b from t1
 ----
 1 1
 2 3
-5 4
+5 4
+
+query I
+select 1
+----
+1