MWL#17: Table elimination

- First code. Elimination works for simple cases, passes the testsuite.
- Known issues:
  = No elimination is done for aggregate functions.
  = EXPLAIN EXTENDED shows eliminated tables (I think it better not)
  = No benchmark yet
  = The code needs some polishing.

mysql-test/r/table_elim.result:
  MWL#17: Table elimination
  - Testcases
mysql-test/t/table_elim.test:
  MWL#17: Table elimination
  - Testcases
sql/sql_select.cc:
  MWL#17: Table elimination
sql/sql_select.h:
  MWL#17: Table elimination
  - Added JOIN_TAB::eliminated (is JOIN_TAB the best place to store this flag?)
sql/table.h:
  MWL#17: Table elimination
  - ADded NESTED_JOIN::n_tables. We need to have the number of real tables remaining in an outer join nest.

1 files changed, 2 insertions, 0 deletions

diff --git a/sql/table.h b/sql/table.h
index 97840d2a1c6..cc54daccf9d 100644
--- a/sql/table.h
+++ b/sql/table.h
@@ -1626,6 +1626,8 @@ typedef struct st_nested_join
     Before each use the counters are zeroed by reset_nj_counters.
   */
   uint              counter;
+  /* Tables left after elimination */
+  uint              n_tables;
   nested_join_map   nj_map;          /* Bit used to identify this nested join*/
 } NESTED_JOIN;