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.

1 files changed, 17 insertions, 0 deletions

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; }