Fix for bug MDEV-3992

Analysis:
  The crash is a result of incorrect analysis of whether a secondary key
  can be extended with a primary in order to compute ORDER BY. The analysis
  is done in test_if_order_by_key(). This function doesn't take into account
  that the primary key may in fact index the same columns as the secondary
  key. For the test query test_if_order_by_key says that there is an extended
  key with total 2 keyparts.
  At the same time, the condition
    if (pkinfo->key_part[i].field->key_start.is_set(nr))
  in test_if_cheaper_oredring() becomes true for (i == 0), which results in
  an invalid access to rec_per_key[-1].
  
Solution:
  The best solution would be to reuse KEY::ext_key_parts that is already computed
  by open_binary_frm(), however after detailed analysis the conclusion is that
  the change would be too intrusive for a GA release.
  The solution for 5.5 is to add a guard for the case when the 0-th key part is
  considered, and to assume that all keys will be scanned in this case.

0 files changed, 0 insertions, 0 deletions