make JOIN::prepare, JOIN::optimize only once for EXPLAIN of derived table

(BUG#2120 sfter merge)


mysql-test/r/derived.result:
  correct results of derived tble EXPLAIN
  test of "Using Index" with derived tables
mysql-test/t/derived.test:
  test of "Using Index" with derived tables
sql/mysql_priv.h:
  way to force derived table save JOIN after execution
sql/sql_derived.cc:
  way to force derived table save JOIN after execution
sql/sql_lex.h:
  way to force derived table save JOIN after execution
sql/sql_select.cc:
  make JOIN::prepare, JOIN::optimize only once for EXPLAIN of derived table

1 files changed, 10 insertions, 0 deletions

diff --git a/mysql-test/t/derived.test b/mysql-test/t/derived.test
index b412555f1e8..988ef30d1dc 100644
--- a/mysql-test/t/derived.test
+++ b/mysql-test/t/derived.test
@@ -192,3 +192,13 @@ CREATE TABLE t1 (name char(1) default NULL, val int(5) default NULL);
 INSERT INTO t1 VALUES ('a',1),  ('a',2),  ('a',2),  ('a',2),  ('a',3),  ('a',6), ('a',7), ('a',11), ('a',11), ('a',12), ('a',13), ('a',13), ('a',20), ('b',2), ('b',3), ('b',4), ('b',5);
 SELECT s.name, AVG(s.val) AS median FROM (SELECT x.name, x.val FROM t1 x, t1 y WHERE x.name=y.name GROUP BY x.name, x.val HAVING SUM(y.val <= x.val) >= COUNT(*)/2 AND SUM(y.val >= x.val) >= COUNT(*)/2) AS s GROUP BY s.name;
 explain SELECT s.name, AVG(s.val) AS median FROM (SELECT x.name, x.val FROM t1 x, t1 y WHERE x.name=y.name GROUP BY x.name, x.val HAVING SUM(y.val <= x.val) >= COUNT(*)/2 AND SUM(y.val >= x.val) >= COUNT(*)/2) AS s GROUP BY s.name;
+drop table t1;
+
+#
+# "Using index" in explain
+#
+create table t2 (a int, b int, primary key (a));
+insert into t2 values (1,7),(2,7);
+explain select a from t2 where a>1;
+explain select a from (select a from t2 where a>1) tt;
+drop table t2;