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().

1 files changed, 9 insertions, 0 deletions

diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index bea3b14e607..634b6d1a3b8 100644
--- a/sql/sql_lex.cc
+++ b/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);