--echo #

--echo # MDEV-17979 Assertion `0' failed in Item::val_native upon SELECT with timestamp, NULLIF, GROUP BY
--echo #

mysql-test/main/timezone2.result

@@ -542,5 +542,18 @@ SELECT * FROM t1 WHERE a IN ((SELECT MAX(b) FROM t1), (SELECT MIN(b) FROM t1));
 a	b
 DROP TABLE t1;
 #
+# MDEV-17979 Assertion `0' failed in Item::val_native upon SELECT with timestamp, NULLIF, GROUP BY
+#
+SET time_zone='+00:00';
+CREATE TABLE t1 (a INT, ts TIMESTAMP) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1, FROM_UNIXTIME(1288481126) /*winter time in Moscow*/);
+SET time_zone='Europe/Moscow';
+CREATE TABLE t2 AS SELECT ts, COALESCE(ts) AS cts FROM t1 GROUP BY cts;
+SELECT ts, cts, UNIX_TIMESTAMP(ts) AS uts, UNIX_TIMESTAMP(cts) AS ucts FROM t2;
+ts	cts	uts	ucts
+2010-10-31 02:25:26	2010-10-31 02:25:26	1288481126	1288481126
+DROP TABLE t1,t2;
+SET time_zone=DEFAULT;
+#
 # End of 10.4 tests
 #

mysql-test/main/timezone2.test

@@ -490,6 +490,18 @@ SELECT * FROM t1 WHERE a = (SELECT MIN(b) FROM t1);
 SELECT * FROM t1 WHERE a IN ((SELECT MAX(b) FROM t1), (SELECT MIN(b) FROM t1));
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-17979 Assertion `0' failed in Item::val_native upon SELECT with timestamp, NULLIF, GROUP BY
+--echo #
+
+SET time_zone='+00:00';
+CREATE TABLE t1 (a INT, ts TIMESTAMP) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1, FROM_UNIXTIME(1288481126) /*winter time in Moscow*/);
+SET time_zone='Europe/Moscow';
+CREATE TABLE t2 AS SELECT ts, COALESCE(ts) AS cts FROM t1 GROUP BY cts;
+SELECT ts, cts, UNIX_TIMESTAMP(ts) AS uts, UNIX_TIMESTAMP(cts) AS ucts FROM t2;
+DROP TABLE t1,t2;
+SET time_zone=DEFAULT;
 
 --echo #
 --echo # End of 10.4 tests

mysql-test/main/type_timestamp.result

@@ -1118,5 +1118,16 @@ ERROR 22007: Incorrect datetime value: '0000-00-00 00:00:00' for column 'a' at r
 DROP TABLE t1;
 SET sql_mode=DEFAULT;
 #
+# MDEV-17979 Assertion `0' failed in Item::val_native upon SELECT with timestamp, NULLIF, GROUP BY
+#
+CREATE TABLE t1 (a INT, b TIMESTAMP) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1,'2018-06-19 00:00:00');
+SELECT NULLIF(b, 'N/A') AS f, MAX(a) FROM t1 GROUP BY f;
+f	MAX(a)
+2018-06-19 00:00:00	1
+Warnings:
+Warning	1292	Truncated incorrect datetime value: 'N/A'
+DROP TABLE t1;
+#
 # End of 10.4 tests
 #

mysql-test/main/type_timestamp.test

@@ -709,6 +709,14 @@ UPDATE t1 SET a=COALESCE(b);
 DROP TABLE t1;
 SET sql_mode=DEFAULT;
 
+--echo #
+--echo # MDEV-17979 Assertion `0' failed in Item::val_native upon SELECT with timestamp, NULLIF, GROUP BY
+--echo #
+
+CREATE TABLE t1 (a INT, b TIMESTAMP) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1,'2018-06-19 00:00:00');
+SELECT NULLIF(b, 'N/A') AS f, MAX(a) FROM t1 GROUP BY f;
+DROP TABLE t1;
 
 --echo #
 --echo # End of 10.4 tests

sql/item.h

@@ -6021,6 +6021,62 @@ public:
 };
 
 
+/**
+  We need a separate class Item_copy_timestamp because
+  TIMESTAMP->string->TIMESTAMP conversion is not round trip safe
+  near the DST change, e.g. '2010-10-31 02:25:26' can mean:
+   - my_time_t(1288477526) - summer time in Moscow
+   - my_time_t(1288481126) - winter time in Moscow, one hour later
+*/
+class Item_copy_timestamp: public Item_copy
+{
+  Timestamp_or_zero_datetime m_value;
+public:
+  Item_copy_timestamp(THD *thd, Item *arg): Item_copy(thd, arg) { }
+  const Type_handler *type_handler() const { return &type_handler_timestamp2; }
+  void copy()
+  {
+    Timestamp_or_zero_datetime_native_null tmp(current_thd, item, false);
+    null_value= tmp.is_null();
+    m_value= tmp.is_null() ? Timestamp_or_zero_datetime() :
+                             Timestamp_or_zero_datetime(tmp);
+  }
+  int save_in_field(Field *field, bool no_conversions)
+  {
+    Timestamp_or_zero_datetime_native native(m_value, decimals);
+    return native.save_in_field(field, decimals);
+  }
+  longlong val_int()
+  {
+    return m_value.to_datetime(current_thd).to_longlong();
+  }
+  double val_real()
+  {
+    return m_value.to_datetime(current_thd).to_double();
+  }
+  String *val_str(String *to)
+  {
+    return m_value.to_datetime(current_thd).to_string(to, decimals);
+  }
+  my_decimal *val_decimal(my_decimal *to)
+  {
+    return m_value.to_datetime(current_thd).to_decimal(to);
+  }
+  bool get_date(THD *thd, MYSQL_TIME *ltime, date_mode_t fuzzydate)
+  {
+    bool res= m_value.to_TIME(thd, ltime, fuzzydate);
+    DBUG_ASSERT(!res);
+    return res;
+  }
+  bool val_native(THD *thd, Native *to)
+  {
+    return m_value.to_native(to, decimals);
+  }
+  Item *get_copy(THD *thd)
+  { return get_item_copy<Item_copy_timestamp>(thd, this); }
+};
+
+
 /*
   Cached_item_XXX objects are not exactly caches. They do the following:
 

sql/sql_select.cc

@@ -23907,7 +23907,7 @@ setup_copy_fields(THD *thd, TMP_TABLE_PARAM *param,
 	 on how the value is to be used: In some cases this may be an
 	 argument in a group function, like: IF(ISNULL(col),0,COUNT(*))
       */
-      if (!(pos=new (thd->mem_root) Item_copy_string(thd, pos)))
+      if (!(pos= pos->type_handler()->create_item_copy(thd, pos)))
 	goto err;
       if (i < border)                           // HAVING, ORDER and GROUP BY
       {

sql/sql_type.cc

@@ -3764,6 +3764,22 @@ Type_handler_date_common::Item_get_cache(THD *thd, const Item *item) const
   return new (thd->mem_root) Item_cache_date(thd);
 }
 
+
+/*************************************************************************/
+
+Item_copy *
+Type_handler::create_item_copy(THD *thd, Item *item) const
+{
+  return new (thd->mem_root) Item_copy_string(thd, item);
+}
+
+
+Item_copy *
+Type_handler_timestamp_common::create_item_copy(THD *thd, Item *item) const
+{
+  return new (thd->mem_root) Item_copy_timestamp(thd, item);
+}
+
 /*************************************************************************/
 
 bool Type_handler_int_result::

sql/sql_type.h

@@ -35,6 +35,7 @@ class Item_const;
 class Item_literal;
 class Item_param;
 class Item_cache;
+class Item_copy;
 class Item_func_or_sum;
 class Item_sum_hybrid;
 class Item_sum_sum;
@@ -3470,6 +3471,7 @@ public:
     DBUG_ASSERT(0);
     return NULL;
   }
+  virtual Item_copy *create_item_copy(THD *thd, Item *item) const;
   virtual int cmp_native(const Native &a, const Native &b) const
   {
     DBUG_ASSERT(0);
@@ -3771,6 +3773,11 @@ public:
   }
   Item *make_const_item_for_comparison(THD *, Item *src, const Item *cmp) const;
   Item_cache *Item_get_cache(THD *thd, const Item *item) const;
+  Item_copy *create_item_copy(THD *thd, Item *item) const
+  {
+    DBUG_ASSERT(0);
+    return NULL;
+  }
   bool set_comparator_func(Arg_comparator *cmp) const;
   bool Item_hybrid_func_fix_attributes(THD *thd,
                                        const char *name,
@@ -5411,6 +5418,7 @@ public:
   int Item_save_in_field(Item *item, Field *field, bool no_conversions) const;
   String *print_item_value(THD *thd, Item *item, String *str) const;
   Item_cache *Item_get_cache(THD *thd, const Item *item) const;
+  Item_copy *create_item_copy(THD *thd, Item *item) const;
   String *Item_func_min_max_val_str(Item_func_min_max *, String *) const;
   double Item_func_min_max_val_real(Item_func_min_max *) const;
   longlong Item_func_min_max_val_int(Item_func_min_max *) const;