MDEV-18072 Assertion `is_null() == item->null_value || conv' failed in...

MDEV-18072 Assertion `is_null() == item->null_value || conv' failed in Timestamp_or_zero_datetime_native_null::Timestamp_or_zero_datetime_native_null upon query with GROUP BY

mysql-test/main/type_timestamp.result

@@ -1143,5 +1143,14 @@ a	dt0	dt6
 DROP TABLE t1;
 SET time_zone=DEFAULT;
 #
+# MDEV-18072 Assertion `is_null() == item->null_value || conv' failed in Timestamp_or_zero_datetime_native_null::Timestamp_or_zero_datetime_native_null upon query with GROUP BY
+#
+CREATE TABLE t1 (t TIMESTAMP);
+INSERT INTO t1 () VALUES (),();
+SELECT IF(0,t,NULL) AS f FROM t1 GROUP BY 'foo';
+f
+NULL
+DROP TABLE t1;
+#
 # End of 10.4 tests
 #

mysql-test/main/type_timestamp.test

@@ -740,6 +740,16 @@ SELECT a, CAST(a AS DATETIME) AS dt0, CAST(a AS DATETIME(6)) AS dt6 FROM t1;
 DROP TABLE t1;
 SET time_zone=DEFAULT;
 
+--echo #
+--echo # MDEV-18072 Assertion `is_null() == item->null_value || conv' failed in Timestamp_or_zero_datetime_native_null::Timestamp_or_zero_datetime_native_null upon query with GROUP BY
+--echo #
+
+CREATE TABLE t1 (t TIMESTAMP);
+INSERT INTO t1 () VALUES (),();
+SELECT IF(0,t,NULL) AS f FROM t1 GROUP BY 'foo';
+DROP TABLE t1;
+
+
 --echo #
 --echo # End of 10.4 tests
 --echo #

sql/item.h

@@ -6032,6 +6032,7 @@ class Item_copy_string : public Item_copy
 class Item_copy_timestamp: public Item_copy
 {
   Timestamp_or_zero_datetime m_value;
+  bool sane() const { return !null_value || m_value.is_zero_datetime(); }
 public:
   Item_copy_timestamp(THD *thd, Item *arg): Item_copy(thd, arg) { }
   const Type_handler *type_handler() const { return &type_handler_timestamp2; }
@@ -6044,34 +6045,47 @@ class Item_copy_timestamp: public Item_copy
   }
   int save_in_field(Field *field, bool no_conversions)
   {
+    DBUG_ASSERT(sane());
+    if (null_value)
+      return set_field_to_null(field);
     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();
+    DBUG_ASSERT(sane());
+    return null_value ? 0 :
+           m_value.to_datetime(current_thd).to_longlong();
   }
   double val_real()
   {
-    return m_value.to_datetime(current_thd).to_double();
+    DBUG_ASSERT(sane());
+    return null_value ? 0e0 :
+           m_value.to_datetime(current_thd).to_double();
   }
   String *val_str(String *to)
   {
-    return m_value.to_datetime(current_thd).to_string(to, decimals);
+    DBUG_ASSERT(sane());
+    return null_value ? NULL :
+           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);
+    DBUG_ASSERT(sane());
+    return null_value ? NULL :
+           m_value.to_datetime(current_thd).to_decimal(to);
   }
   bool get_date(THD *thd, MYSQL_TIME *ltime, date_mode_t fuzzydate)
   {
+    DBUG_ASSERT(sane());
     bool res= m_value.to_TIME(thd, ltime, fuzzydate);
     DBUG_ASSERT(!res);
-    return res;
+    return null_value || res;
   }
   bool val_native(THD *thd, Native *to)
   {
-    return m_value.to_native(to, decimals);
+    DBUG_ASSERT(sane());
+    return null_value || m_value.to_native(to, decimals);
   }
   Item *get_copy(THD *thd)
   { return get_item_copy<Item_copy_timestamp>(thd, this); }