BUG#21635: MYSQL_FIELD struct's member strings seem to misbehave for

expression cols.

The problem was that MYSQL_FIELD::org_name was set for MIN() and MAX()
functions (COUNT() is also mentioned in the bug report but was already
fixed).

After this patch for expressions MYSQL_FIELD::name is set to either
expression itself or its alias, and other data origin fields of
MYSQL_FILED (db, org_table, table, org_name) are empty strings.


sql/item_sum.cc:
  For expressions only col_name should be non-empty string.
tests/mysql_client_test.c:
  Add test case for bug#21635: MYSQL_FIELD struct's member strings seem
  to misbehave for expression cols.

1 files changed, 7 insertions, 3 deletions

diff --git a/sql/item_sum.cc b/sql/item_sum.cc
index 5fd65fecbfc..87c768e9383 100644
--- a/sql/item_sum.cc
+++ b/sql/item_sum.cc
@@ -71,9 +71,13 @@ void Item_sum::make_field(Send_field *tmp_field)
   if (args[0]->type() == Item::FIELD_ITEM && keep_field_type())
   {
     ((Item_field*) args[0])->field->make_field(tmp_field);
-    tmp_field->db_name=(char*)"";
-    tmp_field->org_table_name=tmp_field->table_name=(char*)"";
-    tmp_field->org_col_name=tmp_field->col_name=name;
+    /* For expressions only col_name should be non-empty string. */
+    char *empty_string= (char*)"";
+    tmp_field->db_name= empty_string;
+    tmp_field->org_table_name= empty_string;
+    tmp_field->table_name= empty_string;
+    tmp_field->org_col_name= empty_string;
+    tmp_field->col_name= name;
     if (maybe_null)
       tmp_field->flags&= ~NOT_NULL_FLAG;
   }