bug#23856

4 files changed, 32 insertions, 6 deletions

diff --git a/sql/field.h b/sql/field.h
index 47f61c1fe8b..94c5d94def4 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -1108,6 +1108,11 @@ public:
 
 class Field_varstring :public Field_longstr {
 public:
+  /*
+    The maximum space available in a Field_varstring, in bytes. See
+    length_bytes.
+  */
+  static const int MAX_SIZE= UINT_MAX16;
   /* Store number of bytes used to store length (1 or 2) */
   uint32 length_bytes;
   Field_varstring(char *ptr_arg,
diff --git a/sql/field_conv.cc b/sql/field_conv.cc
index 5670b1e0676..5c74ea9e49f 100644
--- a/sql/field_conv.cc
+++ b/sql/field_conv.cc
@@ -530,7 +530,21 @@ void Copy_field::set(char *to,Field *from)
 }
 
 
+/*
+  To do: 
+
+  If 'save\ is set to true and the 'from' is a blob field, do_copy is set to
+  do_save_blob rather than do_conv_blob.  The only differences between them
+  appears to be:
 
+  - do_save_blob allocates and uses an intermediate buffer before calling 
+    Field_blob::store. Is this in order to trigger the call to 
+    well_formed_copy_nchars, by changing the pointer copy->tmp.ptr()?
+    That call will take place anyway in all known cases.
+
+  - The above causes a truncation to MAX_FIELD_WIDTH. Is this the intended 
+    effect? Truncation is handled by well_formed_copy_nchars anyway.
+ */
 void Copy_field::set(Field *to,Field *from,bool save)
 {
   if (to->type() == FIELD_TYPE_NULL)
diff --git a/sql/item_sum.cc b/sql/item_sum.cc
index 4579ecd48ae..443b3782d6b 100644
--- a/sql/item_sum.cc
+++ b/sql/item_sum.cc
@@ -432,7 +432,7 @@ Field *Item_sum::create_tmp_field(bool group, TABLE *table,
       2-byte lenght. 
     */
     if (max_length/collation.collation->mbmaxlen > 255 && 
-        convert_blob_length < UINT_MAX16 && convert_blob_length)
+        convert_blob_length <= Field_varstring::MAX_SIZE && convert_blob_length)
       return new Field_varstring(convert_blob_length, maybe_null,
                                  name, table,
                                  collation.collation);
@@ -3269,14 +3269,20 @@ bool Item_func_group_concat::setup(THD *thd)
   tmp_table_param->force_copy_fields= force_copy_fields;
   DBUG_ASSERT(table == 0);
   /*
+    Currently we have to force conversion of BLOB values to VARCHAR's
+    if we are to store them in TREE objects used for ORDER BY and
+    DISTINCT. This leads to truncation if the BLOB's size exceeds
+    Field_varstring::MAX_SIZE.
+  */
+  if (arg_count_order > 0 || distinct)
+    set_if_smaller(tmp_table_param->convert_blob_length, 
+                   Field_varstring::MAX_SIZE);
+  /*
     We have to create a temporary table to get descriptions of fields
     (types, sizes and so on).
 
     Note that in the table, we first have the ORDER BY fields, then the
     field list.
-
-    We need to set set_sum_field in true for storing value of blob in buffer
-    of a record instead of a pointer of one.
   */
   if (!(table= create_tmp_table(thd, tmp_table_param, all_fields,
                                 (ORDER*) 0, 0, TRUE,
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 967322600a7..1d8e10ed84b 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -8794,7 +8794,7 @@ Field* create_tmp_field_from_field(THD *thd, Field* org_field,
     Make sure that the blob fits into a Field_varstring which has 
     2-byte lenght. 
   */
-  if (convert_blob_length && convert_blob_length < UINT_MAX16 &&
+  if (convert_blob_length && convert_blob_length <= Field_varstring::MAX_SIZE &&
       (org_field->flags & BLOB_FLAG))
     new_field= new Field_varstring(convert_blob_length,
                                    org_field->maybe_null(),
@@ -8885,7 +8885,8 @@ static Field *create_tmp_field_from_item(THD *thd, Item *item, TABLE *table,
       2-byte lenght. 
     */
     else if (item->max_length/item->collation.collation->mbmaxlen > 255 &&
-             convert_blob_length < UINT_MAX16 && convert_blob_length)
+             convert_blob_length <= Field_varstring::MAX_SIZE && 
+             convert_blob_length)
       new_field= new Field_varstring(convert_blob_length, maybe_null,
                                      item->name, table,
                                      item->collation.collation);