caching of queries with isammerge tables forbiden using general way

SQL_SELECT_LIMIT as default will be applied only for SELECT statement if there was not explicit LIMIT clause
correct table list passed to class constructor of select_update


mysql-test/r/subselect.result:
  do not show limit if it is not explicit
mysql-test/r/union.result:
  test of LIMIT + ORDER
mysql-test/t/union.test:
  test of LIMIT + ORDER
sql/ha_isammrg.h:
  caching of queries with isammerge tables forbiden
sql/sql_cache.cc:
  removed check on isammerge
sql/sql_lex.cc:
  tag of explicit limit in statement
sql/sql_lex.h:
  tag of explicit limit in statement
sql/sql_parse.cc:
  blanks in empty line removed
  no limit by default (SQL_SELECT_LIMIT as default will be applied only for SELECT statement if there was not explicit LIMIT clause)
sql/sql_union.cc:
  reverted incorrect patch
sql/sql_update.cc:
  reverted incorrect patch
  correct table list passed to class constructor
sql/sql_yacc.yy:
  explicit LIMIT marked

1 files changed, 12 insertions, 0 deletions

diff --git a/mysql-test/t/union.test b/mysql-test/t/union.test
index effb0139111..21619534f49 100644
--- a/mysql-test/t/union.test
+++ b/mysql-test/t/union.test
@@ -504,3 +504,15 @@ select 1 union select 2;
 (select 1) union (select 2) union (select 3) limit 2;
 set sql_select_limit=default;
 
+#
+# ORDER with LIMIT
+#
+create table t1 (a int);
+insert into t1 values (100), (1);
+create table t2 (a int);
+insert into t2 values (100);
+select a from t1 union select a from t2 order by a;
+SET SQL_SELECT_LIMIT=1;
+select a from t1 union select a from t2 order by a;
+drop table t1, t2;
+set sql_select_limit=default;