MDEV-32244 Wrong bit encoding using COALESCE

When aggregating pairs BIT+NULL and NULL+BIT for result, e.g.
in COALESCE(), preserve the BIT data type (ignore explicit NULLs).

The same fix applied to YEAR.

mysql-test/main/type_bit.result

@@ -1859,5 +1859,25 @@ cc	18446744073709551615
 cr	18446744073709551615
 ct	18446744073709551615
 #
+# MDEV-32244 Wrong bit encoding using COALESCE
+#
+CREATE TABLE t1 (c1 BIT);
+INSERT INTO t1 (c1) VALUES (0x01);
+CREATE TABLE t2 AS SELECT
+c1,
+COALESCE(c1, c1) AS c2,
+COALESCE(c1, null) AS c3,
+COALESCE(null, c1) AS c4 FROM t1;
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `c1` bit(1) DEFAULT NULL,
+  `c2` bit(1) DEFAULT NULL,
+  `c3` bit(1) DEFAULT NULL,
+  `c4` bit(1) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t2;
+DROP TABLE t1;
+#
 # End of 10.4 tests
 #

mysql-test/main/type_bit.test

@@ -543,6 +543,22 @@ DELIMITER ;$$
 --horizontal_results
 
 
+--echo #
+--echo # MDEV-32244 Wrong bit encoding using COALESCE
+--echo #
+
+CREATE TABLE t1 (c1 BIT);
+INSERT INTO t1 (c1) VALUES (0x01);
+CREATE TABLE t2 AS SELECT
+  c1,
+  COALESCE(c1, c1) AS c2,
+  COALESCE(c1, null) AS c3,
+  COALESCE(null, c1) AS c4 FROM t1;
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+DROP TABLE t1;
+
+
 --echo #
 --echo # End of 10.4 tests
 --echo #

mysql-test/main/type_year.result

@@ -675,5 +675,25 @@ FLOOR(a)	int(4) unsigned	YES		NULL
 CEILING(a)	int(4) unsigned	YES		NULL	
 DROP TABLE t2,t1;
 #
+# MDEV-32244 Wrong bit encoding using COALESCE
+#
+CREATE TABLE t1 (c1 YEAR);
+INSERT INTO t1 (c1) VALUES (0x01);
+CREATE TABLE t2 AS SELECT
+c1,
+COALESCE(c1, c1) AS c2,
+COALESCE(c1, null) AS c3,
+COALESCE(null, c1) AS c4 FROM t1;
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `c1` year(4) DEFAULT NULL,
+  `c2` year(4) DEFAULT NULL,
+  `c3` year(4) DEFAULT NULL,
+  `c4` year(4) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+DROP TABLE t2;
+DROP TABLE t1;
+#
 # End of 10.4 tests
 #

mysql-test/main/type_year.test

@@ -354,6 +354,20 @@ CREATE TABLE t2 AS SELECT a, ROUND(a), TRUNCATE(a,0), FLOOR(a), CEILING(a) FROM
 DESC t2;
 DROP TABLE t2,t1;
 
+--echo #
+--echo # MDEV-32244 Wrong bit encoding using COALESCE
+--echo #
+
+CREATE TABLE t1 (c1 YEAR);
+INSERT INTO t1 (c1) VALUES (0x01);
+CREATE TABLE t2 AS SELECT
+  c1,
+  COALESCE(c1, c1) AS c2,
+  COALESCE(c1, null) AS c3,
+  COALESCE(null, c1) AS c4 FROM t1;
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+DROP TABLE t1;
 
 --echo #
 --echo # End of 10.4 tests

sql/sql_type.cc

@@ -1588,6 +1588,7 @@ Type_handler::bit_and_int_mixture_handler(uint max_char_length)
              Note, independently from "treat_bit_as_number":
              - a single BIT argument gives BIT as a result
              - two BIT couterparts give BIT as a result
+             - (BIT + explicit NULL) or (explicit NULL + BIT) give BIT
 
   @details This function aggregates field types from the array of items.
     Found type is supposed to be used later as the result field type
@@ -1620,8 +1621,11 @@ Type_handler_hybrid_field_type::aggregate_for_result(const char *funcname,
   {
     const Type_handler *cur= items[i]->type_handler();
     set_if_bigger(max_display_length, items[i]->max_display_length());
-    if (treat_bit_as_number &&
+    uint bit_count= (type_handler() == &type_handler_bit) +
-        ((type_handler() == &type_handler_bit) ^ (cur == &type_handler_bit)))
+                    (cur == &type_handler_bit);
+    uint null_count= (type_handler() == &type_handler_null) +
+                     (cur == &type_handler_null);
+    if (treat_bit_as_number && bit_count == 1 && null_count == 0)
     {
       bit_and_non_bit_mixture_found= true;
       if (type_handler() == &type_handler_bit)
@@ -4067,12 +4071,39 @@ Type_handler_timestamp_common::create_item_copy(THD *thd, Item *item) const
 
 /*************************************************************************/
 
+/*
+  This method handles YEAR and BIT data types.
+  It does not switch the data type to DECIAMAL on a
+  unsigned_flag mistmatch. This important for combinations
+  like YEAR+NULL, BIT+NULL.
+*/
 bool Type_handler_int_result::
        Item_hybrid_func_fix_attributes(THD *thd,
                                        const char *func_name,
                                        Type_handler_hybrid_field_type *handler,
                                        Type_all_attributes *func,
                                        Item **items, uint nitems) const
+{
+  func->aggregate_attributes_int(items, nitems);
+  return false;
+}
+
+
+/*
+  This method handles general purpose integer data types
+    TINYINT, SHORTINT, MEDIUNINT, BIGINT.
+  It switches to DECIMAL in case if a mismatch in unsigned_flag found.
+
+  Note, we should fix this to ignore all items with
+  type_handler()==&type_handler_null.
+  It's too late for 10.4. Let's do it eventually in a higher version.
+*/
+bool Type_handler_general_purpose_int::
+       Item_hybrid_func_fix_attributes(THD *thd,
+                                       const char *func_name,
+                                       Type_handler_hybrid_field_type *handler,
+                                       Type_all_attributes *func,
+                                       Item **items, uint nitems) const
 {
   bool unsigned_flag= items[0]->unsigned_flag;
   for (uint i= 1; i < nitems; i++)

sql/sql_type.h

@@ -4820,6 +4820,12 @@ public:
     type_limits_int_by_unsigned_flag(bool unsigned_flag) const= 0;
   uint32 max_display_length(const Item *item) const;
   uint32 Item_decimal_notation_int_digits(const Item *item) const;
+  bool Item_hybrid_func_fix_attributes(THD *thd,
+                                       const char *name,
+                                       Type_handler_hybrid_field_type *,
+                                       Type_all_attributes *atrr,
+                                       Item **items,
+                                       uint nitems) const;
   bool Vers_history_point_resolve_unit(THD *thd, Vers_history_point *p) const;
 };