Fixed bug mdev-5686.

The calls of the function remove_eq_conds() may change the and/or structure
of the where conditions. So JOIN::equal_cond should be updated for non-recursive
calls of remove_eq_conds(). 

mysql-test/r/subselect4.result

@@ -2375,5 +2375,27 @@ ORDER BY v2.id;
 id	a2	a3	id	a2	a3
 DROP VIEW v2;
 DROP TABLE t1,t2;
+#
+# MDEV-5686: degenerate disjunct in NOT IN subquery
+#
+CREATE TABLE t1 (a int, b int, c varchar(3)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1,1,'CAN'),(2,2,'AUS');
+CREATE TABLE t2 (f int) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (3);
+EXPLAIN EXTENDED
+SELECT * FROM t2 
+WHERE f NOT IN (SELECT b FROM t1
+WHERE 0 OR (c IN ('USA') OR c NOT IN ('USA')) AND a = b);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t2	system	NULL	NULL	NULL	NULL	1	100.00	
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select 3 AS `f` from `test`.`t2` where (not(<expr_cache><3>(<in_optimizer>(3,<exists>(select `test`.`t1`.`b` from `test`.`t1` where (((`test`.`t1`.`c` = 'USA') or (`test`.`t1`.`c` <> 'USA')) and trigcond(((<cache>(3) = `test`.`t1`.`b`) or isnull(`test`.`t1`.`b`))) and (`test`.`t1`.`b` = `test`.`t1`.`a`)) having trigcond(<is_not_null_test>(`test`.`t1`.`b`)))))))
+SELECT * FROM t2 
+WHERE f NOT IN (SELECT b FROM t1
+WHERE 0 OR (c IN ('USA') OR c NOT IN ('USA')) AND a = b);
+f
+3
+DROP TABLE t1,t2;
 SET optimizer_switch= @@global.optimizer_switch;
 set @@tmp_table_size= @@global.tmp_table_size;

mysql-test/t/subselect4.test

@@ -1970,5 +1970,26 @@ ORDER BY v2.id;
 DROP VIEW v2;
 DROP TABLE t1,t2;
 
+--echo #
+--echo # MDEV-5686: degenerate disjunct in NOT IN subquery
+--echo #
+
+CREATE TABLE t1 (a int, b int, c varchar(3)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1,1,'CAN'),(2,2,'AUS');
+
+CREATE TABLE t2 (f int) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (3);
+
+EXPLAIN EXTENDED
+SELECT * FROM t2 
+  WHERE f NOT IN (SELECT b FROM t1
+                    WHERE 0 OR (c IN ('USA') OR c NOT IN ('USA')) AND a = b);
+
+SELECT * FROM t2 
+  WHERE f NOT IN (SELECT b FROM t1
+                    WHERE 0 OR (c IN ('USA') OR c NOT IN ('USA')) AND a = b);
+
+DROP TABLE t1,t2;
+
 SET optimizer_switch= @@global.optimizer_switch;
 set @@tmp_table_size= @@global.tmp_table_size;

sql/sql_select.cc

@@ -3530,6 +3530,9 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
   { 
     conds->update_used_tables();
     conds= remove_eq_conds(join->thd, conds, &join->cond_value);
+    if (conds && conds->type() == Item::COND_ITEM &&
+        ((Item_cond*) conds)->functype() == Item_func::COND_AND_FUNC)
+      join->cond_equal= &((Item_cond_and*) conds)->cond_equal;
     join->select_lex->where= conds;
     if (join->cond_value == Item::COND_FALSE)
     {
@@ -13228,7 +13231,10 @@ optimize_cond(JOIN *join, COND *conds,
       Remove all and-levels where CONST item != CONST item
     */
     DBUG_EXECUTE("where",print_where(conds,"after const change", QT_ORDINARY););
-    conds= remove_eq_conds(thd, conds, cond_value) ;
+    conds= remove_eq_conds(thd, conds, cond_value);
+    if (conds && conds->type() == Item::COND_ITEM &&
+        ((Item_cond*) conds)->functype() == Item_func::COND_AND_FUNC)
+      join->cond_equal= &((Item_cond_and*) conds)->cond_equal;
     DBUG_EXECUTE("info",print_where(conds,"after remove", QT_ORDINARY););
   }
   DBUG_RETURN(conds);