1 files changed, 36 insertions, 15 deletions

diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
index f06747b6938..84ba2abf679 100644
--- a/sql/item_cmpfunc.cc
+++ b/sql/item_cmpfunc.cc
@@ -627,17 +627,6 @@ int Arg_comparator::set_compare_func(Item_result_field *item, Item_result type)
   }
   case STRING_RESULT:
   {
-    /*
-      We must set cmp_charset here as we may be called from for an automatic
-      generated item, like in natural join
-    */
-    if (cmp_collation.set((*a)->collation, (*b)->collation) || 
-	cmp_collation.derivation == DERIVATION_NONE)
-    {
-      my_coll_agg_error((*a)->collation, (*b)->collation,
-                        owner->func_name());
-      return 1;
-    }
     if (cmp_collation.collation == &my_charset_bin)
     {
       /*
@@ -761,6 +750,37 @@ bool get_mysql_time_from_str(THD *thd, String *str, timestamp_type warn_type,
 
 
 /**
+  Aggregate comparator argument charsets for comparison.
+  One of the arguments ("a" or "b") can be replaced,
+  typically by Item_string or Item_func_conv_charset.
+
+  @return Aggregation result
+  @retval false - if no conversion is needed,
+                  or if one of the arguments was converted
+  @retval true  - on error, if arguments are not comparable.
+
+  TODO: get rid of this method eventually and refactor the calling code.
+  Argument conversion should happen on the Item_func level.
+  Arg_comparator should get comparable arguments.
+*/
+bool Arg_comparator::agg_arg_charsets_for_comparison()
+{
+  if (cmp_collation.set((*a)->collation, (*b)->collation, MY_COLL_CMP_CONV) ||
+      cmp_collation.derivation == DERIVATION_NONE)
+  {
+    my_coll_agg_error((*a)->collation, (*b)->collation, owner->func_name());
+    return true;
+  }
+  if (agg_item_set_converter(cmp_collation, owner->func_name(),
+                             a, 1, MY_COLL_CMP_CONV, 1) ||
+      agg_item_set_converter(cmp_collation, owner->func_name(),
+                             b, 1, MY_COLL_CMP_CONV, 1))
+    return true;
+  return false;
+}
+
+
+/**
   Prepare the comparator (set the comparison function) for comparing
   items *a1 and *a2 in the context of 'type'.
 
@@ -787,10 +807,11 @@ int Arg_comparator::set_cmp_func(Item_result_field *owner_arg,
       (*a)->result_type() == STRING_RESULT &&
       (*b)->result_type() == STRING_RESULT)
   {
-    DTCollation coll;
-    coll.set((*a)->collation.collation);
-    if (agg_item_set_converter(coll, owner->func_name(),
-                               b, 1, MY_COLL_CMP_CONV, 1))
+    /*
+      We must set cmp_collation here as we may be called from for an automatic
+      generated item, like in natural join
+    */
+    if (agg_arg_charsets_for_comparison())
       return 1;
   }
   if (type == INT_RESULT &&