diff --git a/reconstruct/ast.py b/reconstruct/ast.py
index 3a43c81..8af334e 100644
--- a/reconstruct/ast.py
+++ b/reconstruct/ast.py
@@ -589,13 +589,22 @@ class groupby(ast_node):
     
 class join(ast_node):
     name = 'join'
+    
+    def get_joint_cols(self, cols : List[ColRef]):
+        joint_cols = set()
+        for col in cols:
+            joint_cols |= self.joint_cols[col]
+        return joint_cols
+    
     def init(self, _):
-        self.joins:list = []
+        self.joins : List[join] = []
         self.tables : List[TableInfo] = []
         self.tables_dir = dict()
         self.rec = None
         self.top_level = self.parent and isinstance(self.parent, projection)
         self.have_sep = False
+        self.joint_cols : Dict[ColRef, Set]= dict() # columns that are joined with this column
+        
         # self.tmp_name = 'join_' + base62uuid(4)
         # self.datasource = TableInfo(self.tmp_name, [], self.context)
     def append(self, tbls, __alias = ''):
@@ -690,13 +699,19 @@ class join(ast_node):
         self.sql = ''
         for j in self.joins:
             if not self.sql or j[1]:
-                self.sql += j[0]
+                self.sql += j[0] # using JOIN keyword
             else:
-                self.sql += ', ' + j[0]        
+                self.sql += ', ' + j[0] # using comma
+            for col, jc in j.joint_cols:
+                if col in self.joint_cols:
+                    self.joint_cols[col] |= jc
+                else:
+                    self.joint_cols[col] = set(jc)
+                    
         if node and self.sql and self.top_level:
             self.sql = ' FROM ' + self.sql 
         return super().consume(node)
-    
+        
     def __str__(self):
         return self.sql
     def __repr__(self):
diff --git a/reconstruct/new_expr.py b/reconstruct/new_expr.py
new file mode 100644
index 0000000..a5bc562
--- /dev/null
+++ b/reconstruct/new_expr.py
@@ -0,0 +1,66 @@
+import abc
+from reconstruct.ast import ast_node
+from typing import Optional 
+from reconstruct.storage import Context, ColRef
+from engine.utils import enlist
+from engine.types import builtin_func, user_module_func, builtin_operators
+
+
+class expr_base(ast_node, metaclass = abc.ABCMeta):
+    def __init__(self, parent: Optional["ast_node"], node, context: Optional[Context] = None):
+        self.node = node
+        super().__init__(parent, node, context)
+        
+    def init(self, node):
+        self.is_literal = False
+        self.udf_map = self.context.udf_map
+        self.func_maps = {**builtin_func, **self.udf_map, **user_module_func}
+        self.operators = {**builtin_operators, **self.udf_map, **user_module_func}
+        self.narrow_funcs = ['sum', 'avg', 'count', 'min', 'max', 'last']
+ 
+    def get_literal(self, node):
+        self.is_literal = True
+    
+    def process_child_nodes(self):
+        pass
+    def produce(self, node):
+        from reconstruct.ast import udf
+        if node and type(node) is dict:
+            if 'litral' in node:
+                self.get_literal(node['literal'])
+            else:
+                if len(node) > 1:
+                    raise ValueError(f'Parse Error: more than 1 entry in {node}.')
+                key, val = next(iter(node.items()))
+                if key in self.operators:
+                    self.child_exprs = [__class__(self, v) for v in val]
+                    self.process_child_nodes()
+    def consume(self, _):
+        pass
+    
+    
+class c_expr(expr_base):
+    pass
+
+class sql_expr(expr_base):
+    pass
+
+class udf_expr(c_expr):
+    pass
+
+class proj_expr(c_expr, sql_expr):
+    pass
+
+class orderby_expr(c_expr, sql_expr):
+    pass
+
+class groupby_expr(orderby_expr):
+    pass
+
+class from_expr(sql_expr):
+    pass
+
+class where_expr(sql_expr):
+    pass
+
+
diff --git a/reconstruct/storage.py b/reconstruct/storage.py
index d7e568d..c43131c 100644
--- a/reconstruct/storage.py
+++ b/reconstruct/storage.py
@@ -47,7 +47,7 @@ class TableInfo:
         self.table_name : str = table_name
         self.contextname_cpp : str = ''
         self.alias : Set[str] = set([table_name])
-        self.columns_byname : Dict[str, ColRef] = CaseInsensitiveDict() # column_name, type
+        self.columns_byname : CaseInsensitiveDict[str, ColRef] = CaseInsensitiveDict() # column_name, type
         self.columns : List[ColRef] = []
         self.cxt = cxt
         # keep track of temp vars
@@ -117,7 +117,7 @@ class Context:
         self.queries = []
         self.module_init_loc = 0
         self.special_gb = False
-        
+         
     def __init__(self):
         self.tables_byname = dict()
         self.col_byname = dict()
diff --git a/server/types.h b/server/types.h
index 43d2d1a..d4a5656 100644
--- a/server/types.h
+++ b/server/types.h
@@ -189,6 +189,9 @@ struct astring_view {
 			other_str++;
 		}
 		return !(*this_str || *other_str);
+	}
+	bool operator >(const astring_view&r) const{
+		
 	}
 	operator const char* () const {
 		return reinterpret_cast<const char*>(str);