MDEV-20278 PERCENTILE_DISC() returns a wrong data type

mysql-test/main/win_percentile.test

@@ -146,3 +146,66 @@ select * from v1;
 select median(val) OVER () FROM t1;
 drop table t1;
 drop view v1;
+
+
+--echo #
+--echo # MDEV-20278 PERCENTILE_DISC() returns a wrong data type
+--echo #
+
+--echo # INT variants
+
+CREATE TABLE t1 (name CHAR(30), star_rating INT);
+INSERT INTO t1 VALUES ('Lord of the Ladybirds', 5);
+INSERT INTO t1 VALUES ('Lord of the Ladybirds', 3);
+INSERT INTO t1 VALUES ('Lady of the Flies', 1);
+INSERT INTO t1 VALUES ('Lady of the Flies', 2);
+INSERT INTO t1 VALUES ('Lady of the Flies', 5);
+CREATE OR REPLACE TABLE t2 AS SELECT name, PERCENTILE_DISC(0.5)
+  WITHIN GROUP (ORDER BY star_rating)
+  OVER (PARTITION BY name) AS pc FROM t1;
+SHOW CREATE TABLE t2;
+DROP TABLE t2, t1;
+
+--echo # UNSIGNED INT variants
+
+CREATE OR REPLACE TABLE t1 (name CHAR(30), star_rating BIGINT UNSIGNED);
+INSERT INTO t1 VALUES ('Lord of the Ladybirds', 0x8000000000000005);
+INSERT INTO t1 VALUES ('Lord of the Ladybirds', 0x8000000000000003);
+INSERT INTO t1 VALUES ('Lady of the Flies', 0x8000000000000001);
+INSERT INTO t1 VALUES ('Lady of the Flies', 0x8000000000000002);
+INSERT INTO t1 VALUES ('Lady of the Flies', 0x8000000000000003);
+CREATE OR REPLACE TABLE t2 AS SELECT name, PERCENTILE_DISC(0.5)
+  WITHIN GROUP (ORDER BY star_rating)
+  OVER (PARTITION BY name) AS pc FROM t1;
+SHOW CREATE TABLE t2;
+SELECT name, pc, HEX(pc) FROM t2 ORDER BY name, pc;
+DROP TABLE t2, t1;
+
+--echo # FLOAT variants
+
+CREATE TABLE t1 (name CHAR(30), star_rating FLOAT);
+INSERT INTO t1 VALUES ('Lord of the Ladybirds', 5);
+INSERT INTO t1 VALUES ('Lord of the Ladybirds', 3);
+INSERT INTO t1 VALUES ('Lady of the Flies', 1);
+INSERT INTO t1 VALUES ('Lady of the Flies', 2);
+INSERT INTO t1 VALUES ('Lady of the Flies', 5);
+CREATE TABLE t2 AS SELECT name, PERCENTILE_DISC(0.5)
+  WITHIN GROUP (ORDER BY star_rating)
+  OVER (PARTITION BY name) AS pc FROM t1;
+SHOW CREATE TABLE t2;
+DROP TABLE t2, t1;
+
+--echo # DECIMAL variants
+
+CREATE OR REPLACE TABLE t1 (name CHAR(30), star_rating DECIMAL(30,2));
+INSERT INTO t1 VALUES ('Lord of the Ladybirds', 50000000000);
+INSERT INTO t1 VALUES ('Lord of the Ladybirds', 30000000000);
+INSERT INTO t1 VALUES ('Lady of the Flies', 10000000000);
+INSERT INTO t1 VALUES ('Lady of the Flies', 20000000000);
+INSERT INTO t1 VALUES ('Lady of the Flies', 50000000000);
+CREATE OR REPLACE TABLE t2 AS SELECT name, PERCENTILE_DISC(0.5)
+  WITHIN GROUP (ORDER BY star_rating)
+  OVER (PARTITION BY name) AS pc FROM t1;
+SHOW CREATE TABLE t2;
+SELECT * FROM t2 ORDER BY name, pc;
+DROP TABLE t2, t1;

sql/item_windowfunc.cc

@@ -174,7 +174,8 @@ bool Item_window_func::check_result_type_of_order_item()
 {
   if (only_single_element_order_list())
   {
-    Item_result rtype= window_spec->order_list->first->item[0]->cmp_type();
+    Item *src_item= window_spec->order_list->first->item[0];
+    Item_result rtype= src_item->cmp_type();
     // TODO (varun) : support date type in percentile_cont function
     if (rtype != REAL_RESULT && rtype != INT_RESULT &&
         rtype != DECIMAL_RESULT && rtype != TIME_RESULT)
@@ -182,7 +183,14 @@ bool Item_window_func::check_result_type_of_order_item()
       my_error(ER_WRONG_TYPE_FOR_PERCENTILE_FUNC, MYF(0), window_func()->func_name());
       return TRUE;
     }
-    setting_handler_for_percentile_functions(rtype);
+    if (window_func()->sum_func() == Item_sum::PERCENTILE_DISC_FUNC)
+    {
+      Item_sum_percentile_disc *func=
+        static_cast<Item_sum_percentile_disc*>(window_func());
+      func->set_handler(src_item->type_handler());
+      func->Type_std_attributes::set(src_item);
+      Type_std_attributes::set(src_item);
+    }
   }
   return FALSE;
 }

sql/item_windowfunc.h

@@ -1097,17 +1097,6 @@ class Item_window_func : public Item_func_or_sum
     }
   }
 
-  void setting_handler_for_percentile_functions(Item_result rtype) const
-  {
-    switch (window_func()->sum_func()){
-    case Item_sum::PERCENTILE_DISC_FUNC:
-         ((Item_sum_percentile_disc* ) window_func())->set_handler_by_cmp_type(rtype);
-         break;
-    default:
-      return;
-    }
-  }
-
   bool check_result_type_of_order_item();
 
 

sql/sql_type.h

@@ -3506,10 +3506,6 @@ class Type_handler_hybrid_field_type
   {
     return (m_type_handler= Type_handler::get_handler_by_result_type(type));
   }
-  const Type_handler *set_handler_by_cmp_type(Item_result type)
-  {
-    return (m_type_handler= Type_handler::get_handler_by_cmp_type(type));
-  }
   const Type_handler *set_handler_by_result_type(Item_result type,
                                                  uint max_octet_length,
                                                  CHARSET_INFO *cs)