Support HAVING Clause

Author: JoshInnis

regress/expected/new_cypher.out

@@ -168,6 +168,11 @@ SELECT a.i as j FROM tst a GROUP BY a.i;
 ---
 (0 rows)
 
+SELECT a.i as j FROM tst a GROUP BY a.i HAVING a.i = a.i;
+ j 
+---
+(0 rows)
+
 DROP GRAPH new_cypher CASCADE;
 NOTICE:  drop cascades to 2 other objects
 DETAIL:  drop cascades to table new_cypher._ag_label_vertex

regress/sql/new_cypher.sql

@@ -85,6 +85,7 @@ SELECT a.* FROM tst as a;
 
 SELECT a.i as j FROM tst a GROUP BY a.i;
 
+SELECT a.i as j FROM tst a GROUP BY a.i HAVING a.i = a.i;
 
 DROP GRAPH new_cypher CASCADE;
 DROP GRAPH new_cypher_2 CASCADE;

src/backend/parser/cypher_gram.y

@@ -144,7 +144,7 @@ typedef struct GroupClause
 
 %type <node> where_clause
              a_expr b_expr c_expr indirection_el
-             columnref 
+             columnref having_clause
 
 %type <integer> set_quantifier
 %type <target>	target_el 
@@ -530,7 +530,7 @@ simple_select:
 			SELECT opt_all_clause opt_target_list
 			//into_clause 
             from_clause where_clause group_clause
-			group_clause //having_clause window_clause
+			group_clause having_clause //window_clause
 				{
 					SelectStmt *n = makeNode(SelectStmt);
 					/*n->targetList = $3;
@@ -1295,6 +1295,12 @@ empty_grouping_set:
     }
 ;
 
+having_clause:
+			HAVING a_expr							{ $$ = $2; }
+			| /*EMPTY*/								{ $$ = NULL; }
+		;
+
+
 return:
     RETURN DISTINCT return_item_list group_by_opt having_opt window_clause order_by_opt skip_opt limit_opt
         {