1 files changed, 41 insertions, 0 deletions
diff --git a/sql/item.cc b/sql/item.cc
index a465c2d4e36..bffa7e2990d 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -1179,6 +1179,42 @@ Item *Item::safe_charset_converter(CHARSET_INFO *tocs)
 
 
 /**
+  Some pieces of the code do not support changing of
+  Item_cache to other Item types.
+
+  Example:
+  Item_singlerow_subselect has "Item_cache **row".
+  Creating of Item_func_conv_charset followed by THD::change_item_tree()
+  should not change row[i] from Item_cache directly to Item_func_conv_charset, because Item_singlerow_subselect
+  because Item_singlerow_subselect later calls Item_cache-specific methods,
+  e.g. row[i]->store() and row[i]->cache_value().
+
+  Let's wrap Item_func_conv_charset in a new Item_cache,
+  so the Item_cache-specific methods can still be used for
+  Item_singlerow_subselect::row[i] safely.
+
+  As a bonus we cache the converted value, instead of converting every time
+
+  TODO: we should eventually check all other use cases of change_item_tree().
+  Perhaps some more potentially dangerous substitution examples exist.
+*/
+Item *Item_cache::safe_charset_converter(CHARSET_INFO *tocs)
+{
+  if (!example)
+    return Item::safe_charset_converter(tocs);
+  Item *conv= example->safe_charset_converter(tocs);
+  if (conv == example)
+    return this;
+  Item_cache *cache;
+  if (!conv || !(cache= new Item_cache_str(conv)))
+    return NULL; // Safe conversion is not possible, or OEM
+  cache->setup(conv);
+  cache->fixed= false; // Make Item::fix_fields() happy
+  return cache;
+}
+
+
+/**
   @details
   Created mostly for mysql_prepare_table(). Important
   when a string ENUM/SET column is described with a numeric default value:
@@ -9471,6 +9507,11 @@ bool Item_type_holder::join_types(THD *thd, Item *item)
       item_decimals= 0;
     decimals= MY_MAX(decimals, item_decimals);
   }
+
+  if (fld_type == FIELD_TYPE_GEOMETRY)
+    geometry_type=
+      Field_geom::geometry_type_merge(geometry_type, item->get_geometry_type());
+
   if (Field::result_merge_type(fld_type) == DECIMAL_RESULT)
   {
     decimals= MY_MIN(MY_MAX(decimals, item->decimals), DECIMAL_MAX_SCALE);