Bug #10031 View doesn't use index

Description:
If a view only uses 2nd part of an index for underlying table, it's very slow, even if the first part of index is in where clause of the SELECT FROM VIEW.

Output for explains:
explain select a,b from t1 where a < 2 and b=3 \G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: t1
         type: range
possible_keys: PRIMARY
          key: PRIMARY
      key_len: 4
          ref: NULL
         rows: 4
        Extra: Using where; Using index

explain select a,b from v1 where a < 2 and b=3 \G
*************************** 1. row ***************************
           id: 1
  select_type: PRIMARY
        table: t1
         type: index
possible_keys: PRIMARY
          key: PRIMARY
      key_len: 8
          ref: NULL
         rows: 12
        Extra: Using where; Using index

How to repeat:
CREATE TABLE  t1 (a int, b int, primary key(a,b));

INSERT INTO  t1 VALUES (1,1),(1,2),(1,3),(2,1),(2,2),(2,3),(3,1),(3,2),(3,3), (4,1),(4,2),(4,3);

CREATE VIEW v1 as SELECT a,b FROM t1 WHERE b=3;

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/internals/26486

ChangeSet
  1.2016 05/06/28 07:27:00 igor@rurik.mysql.com +3 -0
  range.result, range.test:
    Added a test case for bug #10031.
  opt_range.cc:
    Fixed bug #10031: range condition was not used with
    views. Range analyzer did not take into account that
    view columns were always referred through Item_ref.

The fix will appear in 5.0.9.

Documented in 5.0.9 changelog.