Bug #46791: Assertion failed:(table->key_read==0),function unknown

function,file sql_base.cc

When uncacheable queries are written to a temp table the optimizer must 
preserve the original JOIN structure, because it is re-using the JOIN 
structure to read from the resulting temporary table.
This was done only for uncacheable sub-queries. 
But top level queries can also benefit from this mechanism, specially if 
they're using index access and need a reset.
Fixed by not limiting the saving of JOIN structure to subqueries
exclusively.
Added a new test file to extend the existing (large) subquery.test.

sql/sql_select.cc

@@ -1474,12 +1474,8 @@ JOIN::optimize()
       }
     }
 
-    /* 
-      If this join belongs to an uncacheable subquery save 
-      the original join 
-    */
-    if (select_lex->uncacheable && !is_top_level_join() &&
-        init_save_join_tab())
+    /* If this join belongs to an uncacheable query save the original join */
+    if (select_lex->uncacheable && init_save_join_tab())
       DBUG_RETURN(-1);                         /* purecov: inspected */
   }