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, 2 insertions, 4 deletions

diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index 19a6941fe32..e545e35921a 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -1023,6 +1023,7 @@ void st_select_lex::init_query()
   ref_pointer_array= 0;
   select_n_having_items= 0;
   prep_where= 0;
+  explicit_limit= 0;
 }
 
 void st_select_lex::init_select()
@@ -1616,10 +1617,7 @@ void st_select_lex::print_limit(THD *thd, String *str)
   if (!thd)
     thd= current_thd;
 
-  if ((select_limit != thd->variables.select_limit &&
-       this == &thd->lex->select_lex) ||
-      (select_limit != HA_POS_ERROR && this != &thd->lex->select_lex) ||
-      offset_limit != 0L)
+  if (explicit_limit)
   {
     str->append(" limit ", 7);
     char buff[20];