A fix and test case for Bug#6050 "EXECUTE stmt reports ambiguous field

names with ident. tables fr. diff. schemata": revise all uses of
Item_field and make them prepared-statements friendly when necessary.


mysql-test/r/ps.result:
  Test results fixed: the test case for Bug#6050
mysql-test/r/ps_1general.result:
  Test results fixed: in prepared statements we expand '*' to a list
  of fully qualified fields (db.table.column).
mysql-test/t/ps.test:
  A test for Bug#6050 "EXECUTE stmt reports ambiguous fieldnames with 
  ident. tables fr. diff. schemata"
sql/item.cc:
  Revise all Item_field constructors: we need to make sure that no Item_field
  object points to unaccessible memory in prepared statements.
sql/item.h:
  Revise all Item_field constructors: we need to make sure that no Item_field
  object points to unaccessible memory in prepared statements.
sql/sql_base.cc:
  Item_field use changed to be prepared statements friendly.
sql/sql_class.h:
  New check of Item_arena state.
sql/sql_union.cc:
  Fixing the problem with name resolving in UNION and prepared statements:
  In case of SELECT a, b, c FROM t1 UNION SELECT a, b, c FROM t2 the list of
  selected items is represented as a List<Item_field>, where each 
  Item_field points to a field of temporary table.
  But the temporary table is created anew on each execution of the prepared 
  statement. So on each subsequent execution we should reset Item_field
  items to point to fields from freshly-created temporary table.
sql/table.h:
  Comment TABLE member.

1 files changed, 21 insertions, 3 deletions

diff --git a/sql/sql_union.cc b/sql/sql_union.cc
index fc2d2a3a5e4..cd1127f9683 100644
--- a/sql/sql_union.cc
+++ b/sql/sql_union.cc
@@ -266,14 +266,14 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
 
   if (first_select->next_select())
   {
-
-  // it is not single select
+    /* This is not a single select */
 
     /*
       Check that it was possible to aggregate
       all collations together for UNION.
     */
     List_iterator_fast<Item> tp(types);
+    Item_arena *arena= thd->current_arena;
     Item *type;
     while ((type= tp++))
     {
@@ -305,7 +305,11 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
     thd_arg->lex->current_select= lex_select_save;
     if (!item_list.elements)
     {
-      Item_arena *arena= thd->current_arena, backup;
+      /*
+        We're in statement prepare or in execution
+        of a conventional statement.
+      */
+      Item_arena backup;
       if (arena->is_stmt_prepare())
 	thd->set_n_backup_item_arena(arena, &backup);
       Field **field;
@@ -345,6 +349,20 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
 	fake_select_lex->table_list.empty();
       }
     }
+    else if (arena->is_stmt_execute())
+    {
+      /*
+        We're in execution of a prepared statement: reset field items
+        to point at fields from the created temporary table.
+      */
+      List_iterator_fast<Item> it(item_list);
+      for (Field **field= table->field; *field; field++)
+      {
+        Item_field *item_field= (Item_field*) it++;
+        DBUG_ASSERT(item_field);
+        item_field->set_field(*field);
+      }
+    }
   }
   else
     first_select->braces= 0; // remove our changes