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, 10 insertions, 3 deletions

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: