Merge pull request #3921 from lichangjiang/pg_patch

Pg patch

src/main/java/com/alibaba/druid/sql/dialect/postgresql/ast/stmt/PGSelectQueryBlock.java

@@ -109,6 +109,9 @@ public class PGSelectQueryBlock extends SQLSelectQueryBlock implements PGSQLObje
     }
 
     public void setOrderBy(SQLOrderBy orderBy) {
+        if (orderBy != null) {
+            orderBy.setParent(this);
+        }
         this.orderBy = orderBy;
     }