bugfix: multi-UPDATE, vcols, const tables

multi-update was setting up read_set/vcol_set in
multi_update::initialize_tables() that is invoked after
the optimizer (JOIN::optimize_inner()). But some rows - if they're from
const tables - will be read already in the optimizer, and these rows
will not have all necessary column/vcol values.

* multi_update::initialize_tables() uses results from the optimizer
  and cannot be moved to be called earlier.
* multi_update::prepare() is called before the optimizer, but
  it cannot set up read_set/vcol_set, because the optimizer
  might reset them (see SELECT_LEX::update_used_tables()).

As a fix I've added a new method, select_result::prepare_to_read_rows(),
it's called from inside the optimizer just before make_join_statistics().

mysql-test/suite/federated/federated_maybe_16324629.result

@@ -13,7 +13,6 @@ insert into t1 values (3, 3), (7, 7);
 delete t1 from t1 where a = 3;
 select * from t1;
 a	b
-3	3
 7	7
 drop table t1;
 connection slave;

mysql-test/suite/vcol/r/update.result

@@ -43,3 +43,14 @@ select * from t1;
 a	b	c
 b	2	b
 drop table t1;
+create table t (a int primary key, b int, c int as (b), index (c));
+insert t (a,b) values (9,0);
+create table t2 select * from t;
+update t, t2 set t.b=10 where t.a=t2.a;
+check table t;
+Table	Op	Msg_type	Msg_text
+test.t	check	status	OK
+select * from t;
+a	b	c
+9	10	10
+drop table t, t2;

mysql-test/suite/vcol/t/update.test

@@ -55,3 +55,13 @@ replace t1 set a = 'a',b =1;
 insert t1 (a,b) values ('a', 1) on duplicate key update a='b', b=2;
 select * from t1;
 drop table t1;
+
+#
+# multi-UPDATE and const tables
+#
+create table t (a int primary key, b int, c int as (b), index (c));
+insert t (a,b) values (9,0);
+create table t2 select * from t;
+update t, t2 set t.b=10 where t.a=t2.a;
+check table t; select * from t;
+drop table t, t2;

sql/sql_class.h

@@ -4455,6 +4455,9 @@ class select_result :public select_result_sink
 #endif
   virtual void update_used_tables() {}
 
+  /* this method is called just before the first row of the table can be read */
+  virtual void prepare_to_read_rows() {}
+
   void reset_offset_limit()
   {
     unit->offset_limit_cnt= 0;
@@ -5301,11 +5304,9 @@ class multi_delete :public select_result_interceptor
   int do_deletes();
   int do_table_deletes(TABLE *table, SORT_INFO *sort_info, bool ignore);
   bool send_eof();
-  inline ha_rows num_deleted()
-  {
-    return deleted;
-  }
+  inline ha_rows num_deleted() const { return deleted; }
   virtual void abort_result_set();
+  void prepare_to_read_rows();
 };
 
 
@@ -5349,16 +5350,11 @@ class multi_update :public select_result_interceptor
   bool initialize_tables (JOIN *join);
   int  do_updates();
   bool send_eof();
-  inline ha_rows num_found()
-  {
-    return found;
-  }
-  inline ha_rows num_updated()
-  {
-    return updated;
-  }
+  inline ha_rows num_found() const { return found; }
+  inline ha_rows num_updated() const { return updated; }
   virtual void abort_result_set();
   void update_used_tables();
+  void prepare_to_read_rows();
 };
 
 class my_var : public Sql_alloc  {

sql/sql_delete.cc

@@ -924,6 +924,15 @@ multi_delete::prepare(List<Item> &values, SELECT_LEX_UNIT *u)
   DBUG_RETURN(0);
 }
 
+void multi_delete::prepare_to_read_rows()
+{
+  /* see multi_update::prepare_to_read_rows() */
+  for (TABLE_LIST *walk= delete_tables; walk; walk= walk->next_local)
+  {
+    TABLE_LIST *tbl= walk->correspondent_table->find_table_for_update();
+    tbl->table->mark_columns_needed_for_delete();
+  }
+}
 
 bool
 multi_delete::initialize_tables(JOIN *join)
@@ -953,7 +962,6 @@ multi_delete::initialize_tables(JOIN *join)
     }
   }
 
-
   walk= delete_tables;
 
   for (JOIN_TAB *tab= first_linear_tab(join, WITHOUT_BUSH_ROOTS,
@@ -977,7 +985,6 @@ multi_delete::initialize_tables(JOIN *join)
 	normal_tables= 1;
       tbl->prepare_triggers_for_delete_stmt_or_event();
       tbl->prepare_for_position();
-      tbl->mark_columns_needed_for_delete();
     }
     else if ((tab->type != JT_SYSTEM && tab->type != JT_CONST) &&
              walk == delete_tables)

sql/sql_lex.cc

@@ -4122,6 +4122,15 @@ void SELECT_LEX::update_used_tables()
           TABLE *tab= tl->table;
           tab->covering_keys= tab->s->keys_for_keyread;
           tab->covering_keys.intersect(tab->keys_in_use_for_query);
+          /*
+            View/derived was merged. Need to recalculate read_set/vcol_set
+            bitmaps here. For example:
+              CREATE VIEW v1 AS SELECT f1,f2,f3 FROM t1;
+              SELECT f1 FROM v1;
+            Initially, the view definition will put all f1,f2,f3 in the
+            read_set for t1. But after the view is merged, only f1 should
+            be in the read_set.
+          */
           bitmap_clear_all(tab->read_set);
           if (tab->vcol_set)
             bitmap_clear_all(tab->vcol_set);

sql/sql_select.cc

@@ -1466,6 +1466,7 @@ JOIN::optimize_inner()
   
   /* Calculate how to do the join */
   THD_STAGE_INFO(thd, stage_statistics);
+  result->prepare_to_read_rows();
   if (make_join_statistics(this, select_lex->leaf_tables, &keyuse) ||
       thd->is_fatal_error)
   {

sql/sql_update.cc

@@ -1800,6 +1800,21 @@ void multi_update::update_used_tables()
   }
 }
 
+void multi_update::prepare_to_read_rows()
+{
+  /*
+    update column maps now. it cannot be done in ::prepare() before the
+    optimizer, because the optimize might reset them (in
+    SELECT_LEX::update_used_tables()), it cannot be done in
+    ::initialize_tables() after the optimizer, because the optimizer
+    might read rows from const tables
+  */
+
+  for (TABLE_LIST *tl= update_tables; tl; tl= tl->next_local)
+    tl->table->mark_columns_needed_for_update();
+}
+
+
 /*
   Check if table is safe to update on fly
 
@@ -1916,12 +1931,10 @@ multi_update::initialize_tables(JOIN *join)
     {
       if (safe_update_on_fly(thd, join->join_tab, table_ref, all_tables))
       {
-        table->mark_columns_needed_for_update();
 	table_to_update= table;			// Update table on the fly
 	continue;
       }
     }
-    table->mark_columns_needed_for_update();
     table->prepare_for_position();
 
     /*