Fix regression in SELECT FROM syntax with WHERE clause

When using 'SELECT FROM table WHERE condition', the query should create
an empty projection (no columns) while still filtering rows. This was
broken by PR apache#17295 which added FROM-first syntax support.

The issue was that both 'FROM table' and 'SELECT FROM table' resulted
in empty projection lists, making them indistinguishable. The fix checks
for the presence of a WHERE clause to differentiate:
- 'FROM table' (no WHERE) -> add wildcard projection (all columns)
- 'SELECT FROM table WHERE ...' -> keep empty projection

Also updates the test expectation to correctly show the empty Projection
node in the query plan.

Fixes apache#17513

Author: adriangb

datafusion/sql/src/select.rs

@@ -79,6 +79,7 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
         let empty_from = matches!(plan, LogicalPlan::EmptyRelation(_));
 
         // Process `where` clause
+        let has_where_clause = select.selection.is_some();
         let base_plan = self.plan_selection(select.selection, plan, planner_context)?;
 
         // Handle named windows before processing the projection expression
@@ -90,6 +91,7 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
             &base_plan,
             select.projection,
             empty_from,
+            has_where_clause,
             planner_context,
         )?;
 
@@ -671,14 +673,19 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
         plan: &LogicalPlan,
         projection: Vec<SelectItem>,
         empty_from: bool,
+        has_where_clause: bool,
         planner_context: &mut PlannerContext,
     ) -> Result<Vec<SelectExpr>> {
         let mut prepared_select_exprs = vec![];
         let mut error_builder = DataFusionErrorBuilder::new();
 
         // Handle the case where no projection is specified but we have a valid FROM clause
-        // In this case, implicitly add a wildcard projection (SELECT *)
-        let projection = if projection.is_empty() && !empty_from {
+        // This happens with FROM-first syntax like "FROM table"
+        // But NOT with "SELECT FROM table WHERE ..." which should have empty projection
+        // When there's a WHERE clause with empty projection, it's "SELECT FROM" syntax
+        // and we should NOT add a wildcard - let the optimizer handle column selection
+        let projection = if projection.is_empty() && !empty_from && !has_where_clause {
+            // FROM-first syntax without WHERE clause - select all columns
             vec![SelectItem::Wildcard(WildcardAdditionalOptions::default())]
         } else {
             projection

datafusion/sqllogictest/test_files/projection.slt

@@ -270,10 +270,12 @@ explain format indent
 select from t1 where t1.a > 1;
 ----
 logical_plan
-01)Filter: t1.a > Int64(1)
-02)--TableScan: t1 projection=[a], partial_filters=[t1.a > Int64(1)]
+01)Projection:
+02)--Filter: t1.a > Int64(1)
+03)----TableScan: t1 projection=[a], partial_filters=[t1.a > Int64(1)]
 physical_plan
-01)CoalesceBatchesExec: target_batch_size=8192
-02)--FilterExec: a@0 > 1
-03)----RepartitionExec: partitioning=RoundRobinBatch(4), input_partitions=1
-04)------DataSourceExec: file_groups={1 group: [[WORKSPACE_ROOT/datafusion/sqllogictest/test_files/scratch/projection/17513.parquet]]}, projection=[a], file_type=parquet, predicate=a@0 > 1, pruning_predicate=a_null_count@1 != row_count@2 AND a_max@0 > 1, required_guarantees=[]
+01)ProjectionExec: expr=[]
+02)--CoalesceBatchesExec: target_batch_size=8192
+03)----FilterExec: a@0 > 1
+04)------RepartitionExec: partitioning=RoundRobinBatch(4), input_partitions=1
+05)--------DataSourceExec: file_groups={1 group: [[WORKSPACE_ROOT/datafusion/sqllogictest/test_files/scratch/projection/17513.parquet]]}, projection=[a], file_type=parquet, predicate=a@0 > 1, pruning_predicate=a_null_count@1 != row_count@2 AND a_max@0 > 1, required_guarantees=[]