Bug #19372:

Added a test case.
The problem was fixed by the fix for bug #17379.
The problem was that because of some conditions 
the optimizer always preferred range or full index
scan access methods to lookup access methods even
when the latter were much cheaper.

mysql-test/r/select.result

@@ -3986,4 +3986,13 @@ t2.access_id IN (1,4) AND t.access_id IS NULL AND t2.faq_id in (265);
 faq_id
 265
 DROP TABLE t1,t2;
+CREATE TABLE t1 (a INT, b INT, KEY inx (b,a));
+INSERT INTO t1 VALUES (1,1), (1,2), (1,3), (1,4), (1,5), (1, 6), (1,7);
+EXPLAIN SELECT COUNT(*) FROM t1 f1 INNER JOIN t1 f2
+ON ( f1.b=f2.b AND f1.a<f2.a ) 
+WHERE 1 AND f1.b NOT IN (100,2232,3343,51111);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	f1	index	inx	inx	10	NULL	7	Using where; Using index
+1	SIMPLE	f2	ref	inx	inx	5	test.f1.b	1	Using where; Using index
+DROP TABLE t1;
 End of 5.0 tests

mysql-test/t/select.test

@@ -3357,4 +3357,17 @@ SELECT t2.faq_id
 
 DROP TABLE t1,t2;
 
+
+#
+# Bug #19372: Optimizer does not use index anymore when WHERE index NOT IN
+# () is added
+#
+CREATE TABLE t1 (a INT, b INT, KEY inx (b,a));
+
+INSERT INTO t1 VALUES (1,1), (1,2), (1,3), (1,4), (1,5), (1, 6), (1,7);
+EXPLAIN SELECT COUNT(*) FROM t1 f1 INNER JOIN t1 f2
+    ON ( f1.b=f2.b AND f1.a<f2.a ) 
+    WHERE 1 AND f1.b NOT IN (100,2232,3343,51111);
+DROP TABLE t1;    
+
 --echo End of 5.0 tests