Fix for bug#49570: Assertion failed: !(order->used & map)

on re-execution of prepared statement

Problem: some (see eq_ref_table()) ORDER BY/GROUP BY optimization
is called before each PS execution. However, we don't properly 
initialize its stucture every time before the call.

Fix: properly initialize the sturture used.

mysql-test/r/ps.result

@@ -1916,4 +1916,26 @@ execute stmt;
 deallocate prepare stmt;
 drop table t1,t2;
 #
+#
+# Bug #49570: Assertion failed: !(order->used & map)
+# on re-execution of prepared statement
+#
+CREATE TABLE t1(a INT PRIMARY KEY);
+INSERT INTO t1 VALUES(0), (1);
+PREPARE stmt FROM 
+"SELECT 1 FROM t1 JOIN t1 t2 USING(a) GROUP BY t2.a, t1.a";
+EXECUTE stmt;
+1
+1
+1
+EXECUTE stmt;
+1
+1
+1
+EXECUTE stmt;
+1
+1
+1
+DEALLOCATE PREPARE stmt;
+DROP TABLE t1;
 End of 5.0 tests.

mysql-test/t/ps.test

@@ -1996,4 +1996,20 @@ deallocate prepare stmt;
 drop table t1,t2;
 --echo #
 
+
+--echo #
+--echo # Bug #49570: Assertion failed: !(order->used & map)
+--echo # on re-execution of prepared statement
+--echo #
+CREATE TABLE t1(a INT PRIMARY KEY);
+INSERT INTO t1 VALUES(0), (1);
+PREPARE stmt FROM 
+  "SELECT 1 FROM t1 JOIN t1 t2 USING(a) GROUP BY t2.a, t1.a";
+EXECUTE stmt;
+EXECUTE stmt;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+DROP TABLE t1;
+
+
 --echo End of 5.0 tests.

sql/sql_select.cc

@@ -6777,6 +6777,7 @@ static void update_depend_map(JOIN *join, ORDER *order)
     table_map depend_map;
     order->item[0]->update_used_tables();
     order->depend_map=depend_map=order->item[0]->used_tables();
+    order->used= 0;
     // Not item_sum(), RAND() and no reference to table outside of sub select
     if (!(order->depend_map & (OUTER_REF_TABLE_BIT | RAND_TABLE_BIT))
         && !order->item[0]->with_sum_func)