Fixed bug#12185: Data type aggregation may produce wrong result

The Item::tmp_table_field_from_field_type() function creates Field_datetime
object instead of Field_timestamp object for timestamp field thus always
changing data type is a tmp table is used.

The Field_blob object constructor which is used in the 
Item::tmp_table_field_from_field_type() is always setting packlength field of
newly created blob to 4. This leads to changing fields data type for example
from the blob to the longblob if a temporary table is used.

The Item::make_string_field() function always converts Field_string objects 
to Field_varstring objects. This leads to changing data type from the 
char/binary to varchar/varbinary.

Added appropriate Field_timestamp object constructor for using in the 
Item::tmp_table_field_from_field_type() function.

Added Field_blob object constructor which sets pack length according to
max_length argument.

The Item::tmp_table_field_from_field_type() function now creates
Field_timestamp object for a timestamp field.

The Item_type_holder::display_length() now returns correct NULL length NULL
length. 

The Item::make_string_field() function now doesn't change Field_string to
Field_varstring in the case of Item_type_holder. 

The Item::tmp_table_field_from_field_type() function now uses the Field_blob
constructor which sets packlength according to max_length.


mysql-test/t/union.test:
  Added test case for bug#12185: Data type aggregation may produce wrong result
  Corrected test case after fix for bug#12185
mysql-test/t/innodb.test:
  Corrected test case after fix for bug#12185
mysql-test/r/union.result:
  Added test case for bug#12185: Data type aggregation may produce wrong result
   Corrected test case after fix for bug#12185
mysql-test/r/innodb.result:
  Corrected test case after fix for bug#12185
mysql-test/r/create.result:
  Corrected the test case after fixing bug#12185
sql/field.h:
  Fixed bug#12185: Data type aggregation may produce wrong result
  Added Field_blob object constructor which sets packlength according to
  max_length argument.
sql/item.cc:
  Fixed bug#12185: Data type aggregation may produce wrong result
  The Item::make_string_field() function now doesn't change Field_string to
  Field_varstring in the case of Item_type_holder.
  The Item::tmp_table_field_from_field_type() function now creates
  Field_timestamp object for a timestamp field.
  The Item::tmp_table_field_from_field_type() function now uses the Field_blob
  constructor which sets packlength according to max_length.
  The Item_type_holder::display_length() now returns correct NULL length NULL
  length.
sql/field.cc:
  Fixed bug#12185: Data type aggregation may produce wrong result
  Added appropriate Field_timestamp object constructor for using in the 
  Item::tmp_table_field_from_field_type() function.

3 files changed, 45 insertions, 3 deletions

diff --git a/sql/field.cc b/sql/field.cc
index a920d6d91b1..163822fe712 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -4484,6 +4484,24 @@ Field_timestamp::Field_timestamp(char *ptr_arg, uint32 len_arg,
 }
 
 
+Field_timestamp::Field_timestamp(bool maybe_null_arg,
+                                 const char *field_name_arg,
+                                 struct st_table *table_arg, CHARSET_INFO *cs)
+  :Field_str((char*) 0, 19, maybe_null_arg ? (uchar*) "": 0, 0,
+	     NONE, field_name_arg, table_arg, cs)
+{
+  /* For 4.0 MYD and 4.0 InnoDB compatibility */
+  flags|= ZEROFILL_FLAG | UNSIGNED_FLAG;
+  if (table && !table->timestamp_field &&
+      unireg_check != NONE)
+  {
+    /* This timestamp has auto-update */
+    table->timestamp_field= this;
+    flags|=TIMESTAMP_FLAG;
+  }
+}
+
+
 /*
   Get auto-set type for TIMESTAMP field.
 
diff --git a/sql/field.h b/sql/field.h
index f4d27e46877..3aeb5e03259 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -781,6 +781,8 @@ public:
 		  enum utype unireg_check_arg, const char *field_name_arg,
 		  struct st_table *table_arg,
 		  CHARSET_INFO *cs);
+  Field_timestamp(bool maybe_null_arg, const char *field_name_arg,
+		 struct st_table *table_arg, CHARSET_INFO *cs);
   enum_field_types type() const { return FIELD_TYPE_TIMESTAMP;}
   enum ha_base_keytype key_type() const { return HA_KEYTYPE_ULONG_INT; }
   enum Item_result cmp_type () const { return INT_RESULT; }
@@ -1129,6 +1131,21 @@ public:
   {
     flags|= BLOB_FLAG;
   }
+  Field_blob(uint32 len_arg,bool maybe_null_arg, const char *field_name_arg,
+	     struct st_table *table_arg, CHARSET_INFO *cs, bool set_packlength)
+    :Field_longstr((char*) 0,len_arg, maybe_null_arg ? (uchar*) "": 0, 0,
+                   NONE, field_name_arg, table_arg, cs)
+  {
+    flags|= BLOB_FLAG;
+    packlength= 4;
+    if (set_packlength)
+    {
+      uint32 char_lengt= len_arg/cs->mbmaxlen;
+      packlength= char_length <= 255 ? 1 :
+                  char_length <= 65535 ? 2 :
+                  char_length <= 16777215 ? 3 : 4;
+    }
+  }
   enum_field_types type() const { return FIELD_TYPE_BLOB;}
   enum ha_base_keytype key_type() const
     { return binary() ? HA_KEYTYPE_VARBINARY2 : HA_KEYTYPE_VARTEXT2; }
diff --git a/sql/item.cc b/sql/item.cc
index 24efc1f106f..c7208a3af64 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -3874,7 +3874,9 @@ Field *Item::make_string_field(TABLE *table)
   if (max_length/collation.collation->mbmaxlen > CONVERT_IF_BIGGER_TO_BLOB)
     return new Field_blob(max_length, maybe_null, name, table,
                           collation.collation);
-  if (max_length > 0)
+  /* Item_type_holder holds the exact type, do not change it */
+  if (max_length > 0 &&
+      (type() != Item::TYPE_HOLDER || field_type() != MYSQL_TYPE_STRING))
     return new Field_varstring(max_length, maybe_null, name, table,
                                collation.collation);
   return new Field_string(max_length, maybe_null, name, table,
@@ -3938,6 +3940,7 @@ Field *Item::tmp_table_field_from_field_type(TABLE *table)
   case MYSQL_TYPE_TIME:
     return new Field_time(maybe_null, name, table, &my_charset_bin);
   case MYSQL_TYPE_TIMESTAMP:
+    return new Field_timestamp(maybe_null, name, table, &my_charset_bin);
   case MYSQL_TYPE_DATETIME:
     return new Field_datetime(maybe_null, name, table, &my_charset_bin);
   case MYSQL_TYPE_YEAR:
@@ -3961,7 +3964,11 @@ Field *Item::tmp_table_field_from_field_type(TABLE *table)
   case MYSQL_TYPE_LONG_BLOB:
   case MYSQL_TYPE_BLOB:
   case MYSQL_TYPE_GEOMETRY:
-    return new Field_blob(max_length, maybe_null, name, table,
+    if (this->type() == Item::TYPE_HOLDER)
+      return new Field_blob(max_length, maybe_null, name, table,
+                          collation.collation, 1);
+    else
+      return new Field_blob(max_length, maybe_null, name, table,
                           collation.collation);
     break;					// Blob handled outside of case
   }
@@ -6117,7 +6124,7 @@ uint32 Item_type_holder::display_length(Item *item)
   case MYSQL_TYPE_DOUBLE:
     return 53;
   case MYSQL_TYPE_NULL:
-    return 4;
+    return 0;
   case MYSQL_TYPE_LONGLONG:
     return 20;
   case MYSQL_TYPE_INT24: