Support SELECT expr;

evadb/binder/statement_binder.py

@@ -150,7 +150,9 @@ def _bind_create_index_statement(self, node: CreateIndexStatement):
 
     @bind.register(SelectStatement)
     def _bind_select_statement(self, node: SelectStatement):
-        self.bind(node.from_table)
+        if node.from_table:
+            self.bind(node.from_table)
+
         if node.where_clause:
             self.bind(node.where_clause)
             if node.where_clause.etype == ExpressionType.COMPARE_LIKE:
@@ -180,7 +182,7 @@ def _bind_select_statement(self, node: SelectStatement):
             self._binder_context = current_context
 
         # chunk_params only supported for DOCUMENT TYPE
-        if node.from_table.chunk_params:
+        if node.from_table and node.from_table.chunk_params:
             assert is_document_table(
                 node.from_table.table.table_obj
             ), "CHUNK related parameters only supported for DOCUMENT tables."

evadb/executor/executor_utils.py

@@ -38,7 +38,7 @@ class ExecutorError(Exception):
 def apply_project(
     batch: Batch, project_list: List[AbstractExpression], catalog: "CatalogManager"
 ):
-    if not batch.empty() and project_list:
+    if batch is None or (not batch.empty() and project_list):
         batches = [expr.evaluate(batch) for expr in project_list]
         batch = Batch.merge_column_wise(batches)
 

evadb/executor/project_executor.py

@@ -16,7 +16,7 @@
 
 from evadb.database import EvaDBDatabase
 from evadb.executor.abstract_executor import AbstractExecutor
-from evadb.executor.executor_utils import apply_project
+from evadb.executor.executor_utils import ExecutorError, apply_project
 from evadb.models.storage.batch import Batch
 from evadb.plan_nodes.project_plan import ProjectPlan
 
@@ -29,9 +29,16 @@ def __init__(self, db: EvaDBDatabase, node: ProjectPlan):
         self.target_list = node.target_list
 
     def exec(self, *args, **kwargs) -> Iterator[Batch]:
-        child_executor = self.children[0]
-        for batch in child_executor.exec(**kwargs):
-            batch = apply_project(batch, self.target_list, self.catalog())
-
+        # SELECT FORECAST(12);
+        if len(self.children) == 0:
+            batch = apply_project(None, self.target_list, self.catalog())
             if not batch.empty():
                 yield batch
+        elif len(self.children) == 1:
+            child_executor = self.children[0]
+            for batch in child_executor.exec(**kwargs):
+                batch = apply_project(batch, self.target_list, self.catalog())
+                if not batch.empty():
+                    yield batch
+        else:
+            raise ExecutorError("ProjectExecutor has more than 1 children.")

evadb/expression/constant_value_expression.py

@@ -33,7 +33,13 @@ def __init__(self, value: Any, v_type: ColumnType = ColumnType.INTEGER):
         self._v_type = v_type
 
     def evaluate(self, batch: Batch, **kwargs):
-        batch = Batch(pd.DataFrame({0: [self._value] * len(batch)}))
+        repeated = 0
+        # SELECT expr;
+        if batch is None:
+            repeated = 1
+        else:
+            repeated = len(batch)
+        batch = Batch(pd.DataFrame({0: [self._value] * repeated}))
         return batch
 
     def signature(self) -> str:

evadb/expression/function_expression.py

@@ -134,7 +134,11 @@ def evaluate(self, batch: Batch, **kwargs) -> Batch:
                 outcomes.modify_column_alias(self.alias)
 
         # record the number of function calls
-        self._stats.num_calls += len(batch)
+        # TODO: should get from the function abstract class.
+        if batch is not None:
+            self._stats.num_calls += len(batch)
+        else:
+            self._stats.num_calls += 1
 
         # try persisting the stats to catalog and do not crash if we fail in doing so
         try:
@@ -187,6 +191,7 @@ def _apply_function_expression(self, func: Callable, batch: Batch, **kwargs):
         if not self._cache:
             return func_args.apply_function_expression(func)
 
+        # TODO: the following cache code does not work for `SELECT func(1);`
         output_cols = [obj.name for obj in self.function_obj.outputs]
 
         # 1. check cache

evadb/optimizer/rules/rules.py

@@ -1176,6 +1176,22 @@ def apply(self, before: LogicalProject, context: OptimizerContext):
         yield after
 
 
+class LogicalProjectNoTableToPhysical(Rule):
+    def __init__(self):
+        pattern = Pattern(OperatorType.LOGICALPROJECT)
+        super().__init__(RuleType.LOGICAL_PROJECT_NO_TABLE_TO_PHYSICAL, pattern)
+
+    def promise(self):
+        return Promise.LOGICAL_PROJECT_NO_TABLE_TO_PHYSICAL
+
+    def check(self, grp_id: int, context: OptimizerContext):
+        return True
+
+    def apply(self, before: LogicalProject, context: OptimizerContext):
+        after = ProjectPlan(before.target_list)
+        yield after
+
+
 class LogicalShowToPhysical(Rule):
     def __init__(self):
         pattern = Pattern(OperatorType.LOGICAL_SHOW)

evadb/optimizer/rules/rules_base.py

@@ -78,6 +78,7 @@ class RuleType(Flag):
     LOGICAL_FUNCTION_SCAN_TO_PHYSICAL = auto()
     LOGICAL_FILTER_TO_PHYSICAL = auto()
     LOGICAL_PROJECT_TO_PHYSICAL = auto()
+    LOGICAL_PROJECT_NO_TABLE_TO_PHYSICAL = auto()
     LOGICAL_SHOW_TO_PHYSICAL = auto()
     LOGICAL_EXPLAIN_TO_PHYSICAL = auto()
     LOGICAL_CREATE_INDEX_TO_VECTOR_INDEX = auto()
@@ -121,6 +122,7 @@ class Promise(IntEnum):
     LOGICAL_FUNCTION_SCAN_TO_PHYSICAL = auto()
     LOGICAL_FILTER_TO_PHYSICAL = auto()
     LOGICAL_PROJECT_TO_PHYSICAL = auto()
+    LOGICAL_PROJECT_NO_TABLE_TO_PHYSICAL = auto()
     LOGICAL_SHOW_TO_PHYSICAL = auto()
     LOGICAL_EXPLAIN_TO_PHYSICAL = auto()
     LOGICAL_CREATE_INDEX_TO_VECTOR_INDEX = auto()

evadb/optimizer/rules/rules_manager.py

@@ -49,6 +49,7 @@
     LogicalLimitToPhysical,
     LogicalLoadToPhysical,
     LogicalOrderByToPhysical,
+    LogicalProjectNoTableToPhysical,
     LogicalProjectToPhysical,
     LogicalProjectToRayPhysical,
     LogicalRenameToPhysical,
@@ -114,6 +115,7 @@ def __init__(self, config: ConfigurationManager):
             LogicalExplainToPhysical(),
             LogicalCreateIndexToVectorIndex(),
             LogicalVectorIndexScanToPhysical(),
+            LogicalProjectNoTableToPhysical(),
         ]
 
         # These rules are enabled only if

evadb/optimizer/statement_to_opr_converter.py

@@ -120,30 +120,28 @@ def visit_select(self, statement: SelectStatement):
         """
 
         table_ref = statement.from_table
-        if table_ref is None:
-            logger.error("From entry missing in select statement")
-            return None
+        if table_ref is not None:
+            self.visit_table_ref(table_ref)
 
-        self.visit_table_ref(table_ref)
+            # Filter Operator
+            predicate = statement.where_clause
+            if predicate is not None:
+                self._visit_select_predicate(predicate)
 
-        # Filter Operator
-        predicate = statement.where_clause
-        if predicate is not None:
-            self._visit_select_predicate(predicate)
+            # TODO ACTION: Group By
 
-        # union
-        if statement.union_link is not None:
-            self._visit_union(statement.union_link, statement.union_all)
+            if statement.groupby_clause is not None:
+                self._visit_groupby(statement.groupby_clause)
 
-        # TODO ACTION: Group By
-        if statement.groupby_clause is not None:
-            self._visit_groupby(statement.groupby_clause)
+            if statement.orderby_list is not None:
+                self._visit_orderby(statement.orderby_list)
 
-        if statement.orderby_list is not None:
-            self._visit_orderby(statement.orderby_list)
+            if statement.limit_count is not None:
+                self._visit_limit(statement.limit_count)
 
-        if statement.limit_count is not None:
-            self._visit_limit(statement.limit_count)
+        # union
+        if statement.union_link is not None:
+            self._visit_union(statement.union_link, statement.union_all)
 
         # Projection operator
         select_columns = statement.target_list
@@ -182,7 +180,8 @@ def _visit_union(self, target, all):
 
     def _visit_projection(self, select_columns):
         projection_opr = LogicalProject(select_columns)
-        projection_opr.append_child(self._plan)
+        if self._plan is not None:
+            projection_opr.append_child(self._plan)
         self._plan = projection_opr
 
     def _visit_select_predicate(self, predicate: AbstractExpression):

evadb/parser/evadb.lark

@@ -150,7 +150,7 @@ alias_clause: AS? uid "(" uid_list ")" | AS? uid
 
 query_expression: "(" query_specification ")" | "(" query_expression ")"
 
-query_specification: SELECT select_elements from_clause order_by_clause? limit_clause?
+query_specification: SELECT select_elements from_clause? order_by_clause? limit_clause?
 
 select_elements: (STAR | select_element ) ("," select_element)*