BUG#826935 Assertion `!table || (!table->read_set ||...

BUG#826935 Assertion `!table || (!table->read_set || bitmap_is_set(table->read_set, field_index))' failed
- add_ref_to_table_cond() should not just overwrite pre_idx_push_select_cond
  with the contents tab->select_cond.
  pre_idx_push_select_cond exists precisely for the reason that it may contain
  a condition that is a strict superset of what is in tab->select_cond. 
  The fix is to inject generated equality into pre_idx_push_select_cond.

mysql-test/r/myisam_icp.result

@@ -224,4 +224,18 @@ set optimizer_switch= @tmp_778434;
 set @myisam_icp_tmp=@@optimizer_switch;
 set optimizer_switch='mrr=on,mrr_sort_keys=on,index_condition_pushdown=on';
 drop table if exists t0, t1, t1i, t1m;
+#
+# BUG#826935 Assertion `!table || (!table->read_set || bitmap_is_set(table->read_set, field_index))' failed
+#
+CREATE TABLE t1 ( a int, b varchar(1024), c int, KEY (c), KEY (c,a)) ;
+INSERT INTO t1 VALUES
+(NULL,'x','-678428672'),
+(NULL,'ok',NULL),
+(796262400,'byluovkgwoukfxedyeffsedajyqkyhpaqqpozn', NULL),
+(7,'STQUF',146014208),
+(955711488,'WWVOR','-1515388928');
+SELECT b FROM t1 WHERE a != 1 AND c IS NULL ORDER BY 1;
+b
+byluovkgwoukfxedyeffsedajyqkyhpaqqpozn
+DROP TABLE t1;
 set optimizer_switch=@myisam_icp_tmp;

mysql-test/t/myisam_icp.test

@@ -195,4 +195,18 @@ drop table if exists t0, t1, t1i, t1m;
 drop table t0, t1, t1i, t1m;
 
 --enable_parsing
+
+--echo #
+--echo # BUG#826935 Assertion `!table || (!table->read_set || bitmap_is_set(table->read_set, field_index))' failed
+--echo #
+CREATE TABLE t1 ( a int, b varchar(1024), c int, KEY (c), KEY (c,a)) ;
+INSERT INTO t1 VALUES
+  (NULL,'x','-678428672'),
+  (NULL,'ok',NULL),
+  (796262400,'byluovkgwoukfxedyeffsedajyqkyhpaqqpozn', NULL),
+  (7,'STQUF',146014208),
+  (955711488,'WWVOR','-1515388928');
+SELECT b FROM t1 WHERE a != 1 AND c IS NULL ORDER BY 1;
+DROP TABLE t1;
+
 set optimizer_switch=@myisam_icp_tmp;

sql/sql_select.cc

@@ -19872,7 +19872,12 @@ static bool add_ref_to_table_cond(THD *thd, JOIN_TAB *join_tab)
       error=(int) cond->add(join_tab->select->cond);
     join_tab->select->cond= cond;
     if (join_tab->select->pre_idx_push_select_cond)
-      join_tab->select->pre_idx_push_select_cond= cond;
+    {
+      Item *new_cond= and_conds(join_tab->select->pre_idx_push_select_cond, cond);
+      if (!new_cond->fixed && new_cond->fix_fields(thd, &new_cond))
+        error= 1;
+      join_tab->select->pre_idx_push_select_cond= new_cond;
+    }
     join_tab->set_select_cond(cond, __LINE__);
   }
   else if ((join_tab->select= make_select(join_tab->table, 0, 0, cond, 0,