diff --git a/lib/ast.ml b/lib/ast.ml
index e5dc4a1..46fc1a4 100644
--- a/lib/ast.ml
+++ b/lib/ast.ml
@@ -2,13 +2,16 @@ type query =
   (*| Select of column list * table list option * filter option*)
   | Select of column list * table_expression
   | CreateSchema of string
-  | CreateTable of table
+  | CreateTable of table_scope option * table
   | DropSchema of string
   | DropTable of table
+  | DropColumn of string
+and table_scope = 
+  | Global
+  | Local
 and column = 
   | Asterisk
-(*  | Column of string *)
-  | Column of expression * as_clause option
+  | Column of expression_primary * as_clause option
 and as_clause =
   | As of string
 and table_expression =
@@ -25,19 +28,18 @@ and join_type =
   | Union
   | Natural
 and condition = 
-  | Condition of predicand * predicate
+  | Condition of expression_primary * predicate
   | And of condition * condition
   | Or of condition * condition
   | Not of condition
-and predicand = expression
 and predicate = 
-  | Comparison of operator * predicand
-  | Between of predicand * predicand
-  | NotBetween of predicand * predicand
-  | In of predicand list
-  | NotIn of predicand list
-  | Like of predicand
-  | NotLike of predicand
+  | Comparison of operator * expression_primary
+  | Between of expression_primary * expression_primary
+  | NotBetween of expression_primary * expression_primary
+  | In of expression_primary list
+  | NotIn of expression_primary list
+  | Like of expression_primary  
+  | NotLike of expression_primary
 and operator =
   | Equals
   | NotEquals
@@ -47,11 +49,11 @@ and operator =
   | GreaterEquals
 and filter = condition
 and group =
-  | Group of quantifier option * expression list option
+  | Group of quantifier option * expression_primary list option
 and aggregate = 
   | Aggregate of func * filter option
 and func =
-  | Function of function_type * quantifier option * expression
+  | Function of function_type * quantifier option * expression_primary
 and function_type = 
   | Avg
   | Max
@@ -61,11 +63,22 @@ and function_type =
 and quantifier = 
   | All
   | Distinct
-and expression = 
+and expression_primary = 
   | Ref of string
   | StringLiteral of string
   | DateLiteral of string
   | TimeLiteral of string
+  | TimestampLiteral of string
+  | Concatenation of expression_primary * expression_primary
+  | Numeric of expression_primary * sign * expression_primary
+  | Signed of sign * expression_primary
+  | Substring of expression_primary * expression_primary
+and sign =
+  | Plus 
+  | Minus
+  | Times
+  | Divide
+
 
 let rec pp_query fmt ast = 
   match ast with
@@ -86,9 +99,11 @@ and pp_column col =
 and pp_expression exp = 
   match exp with 
   | Ref(name) -> name
-  | StringLiteral(name) -> "'"^name^"'"
-  | DateLiteral(name) -> "'"^name^"'"
-  | TimeLiteral(name) -> "'"^name^"'"
+  | StringLiteral(s) -> "'" ^ s ^ "'"
+  | DateLiteral(d) -> "'" ^ d ^ "'"
+  | TimeLiteral(t) -> "'" ^ t ^ "'"
+  | TimestampLiteral(ts) -> "'" ^ ts ^ "'" 
+  | _ -> "Expression not yet supported"
 
 and pp_table_expression table_exp =
   match table_exp with
@@ -137,8 +152,8 @@ and pp_predicate pred =
   | Comparison(op, exp) -> pp_operator op ^ pp_expression exp 
   | Between(exp1, exp2) -> "BETWEEN " ^ pp_expression exp1 ^ " AND " ^pp_expression exp2
   | NotBetween(exp1, exp2) -> "NOT BETWEEN " ^ pp_expression exp1 ^ " AND " ^pp_expression exp2
-  | Like(exp) -> "LIKE " ^ pp_expression exp
-  | NotLike(exp) -> " NOT LIKE " ^ pp_expression exp
+  (*| Like(exp) -> "LIKE " ^ pp_expression exp
+  | NotLike(exp) -> " NOT LIKE " ^ pp_expression exp*)
   | _ -> failwith "Predicate not supported"
 
 and pp_operator op =