Don't try to open temporary tables if there are no temporary tables.

This was done to increase performance when not using temporary tables
as checking if a table is a temporary table involves a lot of code.

sql/sql_base.cc

@@ -3691,9 +3691,9 @@ open_and_process_table(THD *thd, TABLE_LIST *tables, uint *counter, uint flags,
         The problem is that since those attributes are not set in merge
         children, another round of PREPARE will not help.
     */
-    error= thd->open_temporary_table(tables);
-
-    if (!error && !tables->table)
+    if (!thd->has_temporary_tables() ||
+        (!(error= thd->open_temporary_table(tables)) &&
+         !tables->table))
       error= open_table(thd, tables, ot_ctx);
 
     thd->pop_internal_handler();
@@ -3710,9 +3710,9 @@ open_and_process_table(THD *thd, TABLE_LIST *tables, uint *counter, uint flags,
     Repair_mrg_table_error_handler repair_mrg_table_handler;
     thd->push_internal_handler(&repair_mrg_table_handler);
 
-    error= thd->open_temporary_table(tables);
-
-    if (!error && !tables->table)
+    if (!thd->has_temporary_tables() ||
+        (!(error= thd->open_temporary_table(tables)) &&
+         !tables->table))
       error= open_table(thd, tables, ot_ctx);
 
     thd->pop_internal_handler();
@@ -3727,7 +3727,8 @@ open_and_process_table(THD *thd, TABLE_LIST *tables, uint *counter, uint flags,
         still might need to look for a temporary table if this table
         list element corresponds to underlying table of a merge table.
       */
-      error= thd->open_temporary_table(tables);
+      if (thd->has_temporary_tables())
+        error= thd->open_temporary_table(tables);
     }
 
     if (!error && !tables->table)

sql/sql_class.h

@@ -4851,6 +4851,7 @@ class THD: public THD_count, /* this must be first */
     TMP_TABLE_ANY
   };
   bool has_thd_temporary_tables();
+  bool has_temporary_tables();
 
   TABLE *create_and_open_tmp_table(LEX_CUSTRING *frm,
                                    const char *path,
@@ -4889,7 +4890,6 @@ class THD: public THD_count, /* this must be first */
   /* Whether a lock has been acquired? */
   bool m_tmp_tables_locked;
 
-  bool has_temporary_tables();
   uint create_tmp_table_def_key(char *key, const char *db,
                                 const char *table_name);
   TMP_TABLE_SHARE *create_temporary_table(LEX_CUSTRING *frm,

sql/sql_cte.cc

@@ -834,6 +834,7 @@ st_select_lex_unit *With_element::clone_parsed_spec(THD *thd,
   st_select_lex_unit *res= NULL; 
   Query_arena backup;
   Query_arena *arena= thd->activate_stmt_arena_if_needed(&backup);
+  bool has_tmp_tables;
 
   if (!(lex= (LEX*) new(thd->mem_root) st_lex_local))
   {
@@ -879,11 +880,12 @@ st_select_lex_unit *With_element::clone_parsed_spec(THD *thd,
 
   spec_tables= lex->query_tables;
   spec_tables_tail= 0;
+  has_tmp_tables= thd->has_temporary_tables();
   for (TABLE_LIST *tbl= spec_tables;
        tbl;
        tbl= tbl->next_global)
   {
-    if (!tbl->derived && !tbl->schema_table &&
+    if (has_tmp_tables && !tbl->derived && !tbl->schema_table &&
         thd->open_temporary_table(tbl))
       goto err;
     spec_tables_tail= tbl;

sql/temporary_tables.cc

@@ -338,9 +338,11 @@ bool THD::open_temporary_table(TABLE_LIST *tl)
     have invalid db or table name.
     Instead THD::open_tables() should be used.
   */
-  DBUG_ASSERT(!tl->derived && !tl->schema_table);
+  DBUG_ASSERT(!tl->derived);
+  DBUG_ASSERT(!tl->schema_table);
+  DBUG_ASSERT(has_temporary_tables());
 
-  if (tl->open_type == OT_BASE_ONLY || !has_temporary_tables())
+  if (tl->open_type == OT_BASE_ONLY)
   {
     DBUG_PRINT("info", ("skip_temporary is set or no temporary tables"));
     DBUG_RETURN(false);
@@ -452,10 +454,13 @@ bool THD::open_temporary_table(TABLE_LIST *tl)
 */
 bool THD::open_temporary_tables(TABLE_LIST *tl)
 {
+  TABLE_LIST *first_not_own;
   DBUG_ENTER("THD::open_temporary_tables");
 
-  TABLE_LIST *first_not_own= lex->first_not_own_table();
+  if (!has_temporary_tables())
+    DBUG_RETURN(0);
 
+  first_not_own= lex->first_not_own_table();
   for (TABLE_LIST *table= tl; table && table != first_not_own;
        table= table->next_global)
   {
@@ -868,7 +873,7 @@ void THD::restore_tmp_table_share(TMP_TABLE_SHARE *share)
   @return false                       Temporary tables exist
           true                        No temporary table exist
 */
-inline bool THD::has_temporary_tables()
+bool THD::has_temporary_tables()
 {
   DBUG_ENTER("THD::has_temporary_tables");
   bool result= (rgi_slave