Added the median function to the parser , it should behave as a...

Added the median function to the parser , it should behave as a percentile_cont function with its argument fixed to 0.5

sql/lex.h

@@ -737,6 +737,7 @@ static SYMBOL sql_functions[] = {
   { "LAG",              SYM(LAG_SYM)},
   { "LEAD",             SYM(LEAD_SYM)},
   { "MAX",		SYM(MAX_SYM)},
+  { "MEDIAN", SYM(MEDIAN_SYM)},
   { "MID",		SYM(SUBSTRING)},	/* unireg function */
   { "MIN",		SYM(MIN_SYM)},
   { "NOW",		SYM(NOW_SYM)},

sql/sql_yacc.yy

@@ -1236,6 +1236,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
 %token  MAX_STATEMENT_TIME_SYM
 %token  MAX_USER_CONNECTIONS_SYM
 %token  MAXVALUE_SYM                 /* SQL-2003-N */
+%token  MEDIAN_SYM
 %token  MEDIUMBLOB
 %token  MEDIUMINT
 %token  MEDIUMTEXT
@@ -1737,6 +1738,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
         window_func
         simple_window_func
         inverse_distribution_function
+        percentile_function
         inverse_distribution_function_def
         function_call_keyword
         function_call_nonkeyword
@@ -10703,12 +10705,11 @@ simple_window_func:
           }
         ;
 
+
+
 inverse_distribution_function:
-          inverse_distribution_function_def WITHIN GROUP_SYM
-          '('
-           { Select->prepare_add_window_spec(thd); }
-           order_by_single_element_list ')' OVER_SYM
-          '(' opt_window_ref opt_window_partition_clause ')'
+          percentile_function OVER_SYM
+          '(' opt_window_partition_clause ')'
           {
             LEX *lex= Lex;
             if (Select->add_window_spec(thd, lex->win_ref,
@@ -10725,6 +10726,29 @@ inverse_distribution_function:
           }
         ;
 
+percentile_function:
+          inverse_distribution_function_def  WITHIN GROUP_SYM '('
+           { Select->prepare_add_window_spec(thd); }
+           order_by_single_element_list ')'
+           {
+             $$= $1;
+           }
+        | MEDIAN_SYM '(' expr ')'
+          {
+            Item *args= new (thd->mem_root) Item_decimal(thd, "0.5", 3,
+                                                   thd->charset());
+            if (($$ == NULL) || (thd->is_error()))
+            {
+              MYSQL_YYABORT;
+            }
+            if (add_order_to_list(thd, $3,FALSE)) MYSQL_YYABORT;
+
+            $$= new (thd->mem_root) Item_sum_percentile_cont(thd, args);
+            if ($$ == NULL)
+              MYSQL_YYABORT;
+          }
+        ;
+
 inverse_distribution_function_def:
           PERCENTILE_CONT_SYM '(' expr ')'
           {