Fix for Bug#5034 "prepared "select 1 into @arg15", second

execute crashes server": we were deleting lex->result
after each execute, but prepared statements assumed that
it's left intact.
The fix adds cleanup() method to select_result hierarchy,
so that result objects can be reused.
Plus we now need to delete result objects more wisely.


mysql-test/r/ps.result:
  Test results fixed: test case for bug#5034
mysql-test/t/ps.test:
  A test case for bug#5034, few followups
sql/sql_class.cc:
  - fix warning in THD::THD
  - implementation of cleanup() for select_result hierarchy
  - select_export::send_eof was identical to 
    select_dump::send_eof: moved to the base class select_to_file.
  - Statement::end_statement() to end lex, free items, and
    delete possible select_result
sql/sql_class.h:
  - select_result::cleanup() declaration
  -
sql/sql_insert.cc:
  - implementation of select_insert::cleanup(): currently
    we always create a new instance of select_insert/
    select_create on each execute.
sql/sql_lex.cc:
  - with more complicated logic of freeing lex->result it's 
    easier to have it non-zero only if it points to a valid
    result.
sql/sql_lex.h:
  Now st_lex::st_lex is not empty.
sql/sql_parse.cc:
  mysql_execute_command():
  - delete select_result *result only if it was created in
    this function.
  - use end_statement() to cleanup lex and thd in the end of
    each statement.
  - no need to save THD::lock if this is explain. This save
    apparently left from times when derived tables were 
    materialized here, not in open_and_lock_tables.
sql/sql_prepare.cc:
  - call result->cleanup() in reset_stmt_for_execute
  - now Statement is responsible for freeing its lex->result.
sql/sql_select.cc:
  handle_select():
  - don't delete result, it might be needed
    for next executions
  - result is never null

1 files changed, 6 insertions, 2 deletions

diff --git a/sql/sql_prepare.cc b/sql/sql_prepare.cc
index 850d41a030b..6d494b83535 100644
--- a/sql/sql_prepare.cc
+++ b/sql/sql_prepare.cc
@@ -1630,7 +1630,8 @@ int mysql_stmt_prepare(THD *thd, char *packet, uint packet_length,
 static void reset_stmt_for_execute(Prepared_statement *stmt)
 {
   THD *thd= stmt->thd;
-  SELECT_LEX *sl= stmt->lex->all_selects_list;
+  LEX *lex= stmt->lex;
+  SELECT_LEX *sl= lex->all_selects_list;
 
   for (; sl; sl= sl->next_select_in_list())
   {
@@ -1678,7 +1679,9 @@ static void reset_stmt_for_execute(Prepared_statement *stmt)
       unit->reinit_exec_mechanism();
     }
   }
-  stmt->lex->current_select= &stmt->lex->select_lex;
+  lex->current_select= &lex->select_lex;
+  if (lex->result)
+    lex->result->cleanup();
 }
 
 
@@ -2053,6 +2056,7 @@ void Prepared_statement::setup_set_params()
 Prepared_statement::~Prepared_statement()
 {
   free_items(free_list);
+  delete lex->result;
 }