MDEV-7005 NULLIF does not work as documented

MDEV-7146 NULLIF returns unexpected result with a YEAR field

mysql-test/r/ctype_binary.result

@@ -2900,7 +2900,7 @@ SHOW CREATE TABLE t2;
 Table	Create Table
 t2	CREATE TABLE `t2` (
   `d` date DEFAULT NULL,
-  `bad` varbinary(10) DEFAULT NULL
+  `bad` date DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1, t2;
 SET NAMES latin1;

mysql-test/r/ctype_cp1251.result

@@ -3292,7 +3292,7 @@ SHOW CREATE TABLE t2;
 Table	Create Table
 t2	CREATE TABLE `t2` (
   `d` date DEFAULT NULL,
-  `bad` varchar(10) CHARACTER SET cp1251 DEFAULT NULL
+  `bad` date DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1, t2;
 SET NAMES latin1;

mysql-test/r/ctype_latin1.result

@@ -3576,7 +3576,7 @@ SHOW CREATE TABLE t2;
 Table	Create Table
 t2	CREATE TABLE `t2` (
   `d` date DEFAULT NULL,
-  `bad` varchar(10) DEFAULT NULL
+  `bad` date DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1, t2;
 SET NAMES latin1;

mysql-test/r/ctype_ucs.result

@@ -4483,7 +4483,7 @@ SHOW CREATE TABLE t2;
 Table	Create Table
 t2	CREATE TABLE `t2` (
   `d` date DEFAULT NULL,
-  `bad` varchar(10) CHARACTER SET ucs2 DEFAULT NULL
+  `bad` date DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1, t2;
 SET NAMES latin1;

mysql-test/r/ctype_utf8.result

@@ -5351,7 +5351,7 @@ SHOW CREATE TABLE t2;
 Table	Create Table
 t2	CREATE TABLE `t2` (
   `d` date DEFAULT NULL,
-  `bad` varchar(10) CHARACTER SET utf8 DEFAULT NULL
+  `bad` date DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1, t2;
 SET NAMES latin1;

sql/item_cmpfunc.cc

@@ -525,6 +525,32 @@ static bool convert_const_to_int(THD *thd, Item_field *field_item,
 }
 
 
+/*
+  Make a special case of compare with fields to get nicer comparisons
+  of bigint numbers with constant string.
+  This directly contradicts the manual (number and a string should
+  be compared as doubles), but seems to provide more
+  "intuitive" behavior in some cases (but less intuitive in others).
+*/
+void Item_func::convert_const_compared_to_int_field(THD *thd)
+{
+  DBUG_ASSERT(arg_count == 2);
+  if (!thd->lex->is_ps_or_view_context_analysis())
+  {
+    int field;
+    if (args[field= 0]->real_item()->type() == FIELD_ITEM ||
+        args[field= 1]->real_item()->type() == FIELD_ITEM)
+    {
+      Item_field *field_item= (Item_field*) (args[field]->real_item());
+      if ((field_item->field_type() ==  MYSQL_TYPE_LONGLONG ||
+           field_item->field_type() ==  MYSQL_TYPE_YEAR) &&
+          convert_const_to_int(thd, field_item, &args[!field]))
+        args[0]->cmp_context= args[1]->cmp_context= INT_RESULT;
+    }
+  }
+}
+
+
 void Item_bool_func2::fix_length_and_dec()
 {
   max_length= 1;				     // Function returns 0 or 1
@@ -557,29 +583,9 @@ void Item_bool_func2::fix_length_and_dec()
   args[0]->cmp_context= args[1]->cmp_context=
     item_cmp_type(args[0]->result_type(), args[1]->result_type());
 
-  /*
-    Make a special case of compare with fields to get nicer comparisons
-    of bigint numbers with constant string.
-    This directly contradicts the manual (number and a string should
-    be compared as doubles), but seems to provide more
-    "intuitive" behavior in some cases (but less intuitive in others).
-
-    But disable conversion in case of LIKE function.
-  */
-  THD *thd= current_thd;
-  if (functype() != LIKE_FUNC && !thd->lex->is_ps_or_view_context_analysis())
-  {
-    int field;
-    if (args[field= 0]->real_item()->type() == FIELD_ITEM ||
-        args[field= 1]->real_item()->type() == FIELD_ITEM)
-    {
-      Item_field *field_item= (Item_field*) (args[field]->real_item());
-      if ((field_item->field_type() ==  MYSQL_TYPE_LONGLONG ||
-           field_item->field_type() ==  MYSQL_TYPE_YEAR) &&
-          convert_const_to_int(thd, field_item, &args[!field]))
-        args[0]->cmp_context= args[1]->cmp_context= INT_RESULT;
-    }
-  }
+  //  Convert constants when compared to int/year field, unless this is LIKE
+  if (functype() != LIKE_FUNC)
+    convert_const_compared_to_int_field(current_thd);
   set_cmp_func();
 }
 
@@ -2723,18 +2729,21 @@ bool Item_func_if::date_op(MYSQL_TIME *ltime, uint fuzzydate)
 void
 Item_func_nullif::fix_length_and_dec()
 {
-  Item_bool_func2::fix_length_and_dec();
+  if (!args[0])					// Only false if EOM
+    return;
+
+  cached_result_type= args[0]->result_type();
+  cached_field_type= args[0]->field_type();
+  collation.set(args[0]->collation);
+  decimals= args[0]->decimals;
+  unsigned_flag= args[0]->unsigned_flag;
+  fix_char_length(args[0]->max_char_length());
+
+  convert_const_compared_to_int_field(current_thd);
+  args[0]->cmp_context= args[1]->cmp_context=
+    item_cmp_type(args[0]->result_type(), args[1]->result_type());
+  cmp.set_cmp_func(this, tmp_arg, tmp_arg + 1, args[0]->cmp_context);
   maybe_null=1;
-  if (args[0])					// Only false if EOM
-  {
-    decimals=args[0]->decimals;
-    unsigned_flag= args[0]->unsigned_flag;
-    cached_result_type= args[0]->result_type();
-    if (cached_result_type == STRING_RESULT &&
-        agg_arg_charsets_for_comparison(collation, args, arg_count))
-      return;
-    fix_char_length(args[0]->max_char_length());
-  }
 }
 
 
@@ -2749,7 +2758,7 @@ Item_func_nullif::fix_length_and_dec()
 */
 
 double
-Item_func_nullif::val_real()
+Item_func_nullif::real_op()
 {
   DBUG_ASSERT(fixed == 1);
   double value;
@@ -2758,13 +2767,13 @@ Item_func_nullif::val_real()
     null_value=1;
     return 0.0;
   }
-  value= args[0]->val_real();
-  null_value=args[0]->null_value;
+  value= m_args0_copy->val_real();
+  null_value=m_args0_copy->null_value;
   return value;
 }
 
 longlong
-Item_func_nullif::val_int()
+Item_func_nullif::int_op()
 {
   DBUG_ASSERT(fixed == 1);
   longlong value;
@@ -2773,13 +2782,13 @@ Item_func_nullif::val_int()
     null_value=1;
     return 0;
   }
-  value=args[0]->val_int();
-  null_value=args[0]->null_value;
+  value=m_args0_copy->val_int();
+  null_value=m_args0_copy->null_value;
   return value;
 }
 
 String *
-Item_func_nullif::val_str(String *str)
+Item_func_nullif::str_op(String *str)
 {
   DBUG_ASSERT(fixed == 1);
   String *res;
@@ -2788,14 +2797,14 @@ Item_func_nullif::val_str(String *str)
     null_value=1;
     return 0;
   }
-  res=args[0]->val_str(str);
-  null_value=args[0]->null_value;
+  res=m_args0_copy->val_str(str);
+  null_value=m_args0_copy->null_value;
   return res;
 }
 
 
 my_decimal *
-Item_func_nullif::val_decimal(my_decimal * decimal_value)
+Item_func_nullif::decimal_op(my_decimal * decimal_value)
 {
   DBUG_ASSERT(fixed == 1);
   my_decimal *res;
@@ -2804,16 +2813,26 @@ Item_func_nullif::val_decimal(my_decimal * decimal_value)
     null_value=1;
     return 0;
   }
-  res= args[0]->val_decimal(decimal_value);
-  null_value= args[0]->null_value;
+  res= m_args0_copy->val_decimal(decimal_value);
+  null_value= m_args0_copy->null_value;
   return res;
 }
 
 
+bool
+Item_func_nullif::date_op(MYSQL_TIME *ltime, uint fuzzydate)
+{
+  DBUG_ASSERT(fixed == 1);
+  if (!cmp.compare())
+    return (null_value= true);
+  return (null_value= m_args0_copy->get_date(ltime, fuzzydate));
+}
+
+
 bool
 Item_func_nullif::is_null()
 {
-  return (null_value= (!cmp.compare() ? 1 : args[0]->null_value)); 
+  return (null_value= (!cmp.compare() ? 1 : m_args0_copy->null_value)); 
 }
 
 

sql/item_cmpfunc.h

@@ -822,20 +822,30 @@ class Item_func_if :public Item_func_case_abbreviation2
 };
 
 
-class Item_func_nullif :public Item_bool_func2
+class Item_func_nullif :public Item_func_hybrid_field_type
 {
-  enum Item_result cached_result_type;
+  Arg_comparator cmp;
+  /*
+    Remember the first argument in case it will be substituted by either of:
+    - convert_const_compared_to_int_field()
+    - agg_item_set_converter() in set_cmp_func()
+    - cache_converted_constant() in set_cmp_func()
+    The original item will be stored in m_arg0_copy, to return result.
+    The substituted item will be stored in args[0], for comparison purposes.
+  */
+  Item *m_args0_copy;
 public:
   Item_func_nullif(Item *a,Item *b)
-    :Item_bool_func2(a,b), cached_result_type(INT_RESULT)
+    :Item_func_hybrid_field_type(a, b),
+     m_args0_copy(a)
   {}
-  double val_real();
-  longlong val_int();
-  String *val_str(String *str);
-  my_decimal *val_decimal(my_decimal *);
-  enum Item_result result_type () const { return cached_result_type; }
+  bool date_op(MYSQL_TIME *ltime, uint fuzzydate);
+  double real_op();
+  longlong int_op();
+  String *str_op(String *str);
+  my_decimal *decimal_op(my_decimal *);
   void fix_length_and_dec();
-  uint decimal_precision() const { return args[0]->decimal_precision(); }
+  uint decimal_precision() const { return m_args0_copy->decimal_precision(); }
   const char *func_name() const { return "nullif"; }
 
   virtual inline void print(String *str, enum_query_type query_type)

sql/item_func.h

@@ -396,6 +396,7 @@ class Item_func :public Item_result_field
     info.bool_function= &Item::restore_to_before_no_rows_in_result;
     walk(&Item::call_bool_func_processor, FALSE, (uchar*) &info);
   }
+  void convert_const_compared_to_int_field(THD *thd);
 };