Bug#8670

  Rework to resolve ambigious grammer: conflict in join expression
  handling of parentheses for nested joins and derived tables.
  Tests included of failing statements
Optimize item construction for AND/OR logical expressions


mysql-test/r/select.result:
  Bug#8670
    Tests for failing expressions
mysql-test/t/select.test:
  Bug#8670
    Tests for failing expressions
sql/sql_parse.cc:
  Bug#8670
    method st_select_lex::end_nested_join() returns NULL when
    there are no elements in the join.
sql/sql_yacc.yy:
  Optimize construction for Item_cond_or and Item_cond_and
    Reduces object count in case of complex expressions.
  Bug#8670
    Solve ambigious grammar.
    Fix handling of parentheses in join expressions to
    correct handling of nested joins and derived tables.

mysql-test/r/select.result

@@ -2446,3 +2446,12 @@ cast((a - b) as unsigned)
 1
 18446744073709551615
 drop table t1;
+create table t1 (a int, b int);
+create table t2 like t1;
+select t1.a from (t1 inner join t2 on t1.a=t2.a) where t2.a=1;
+a
+select t1.a from ((t1 inner join t2 on t1.a=t2.a)) where t2.a=1;
+a
+select x.a, y.a, z.a from ( (t1 x inner join t2 y on x.a=y.a) inner join t2 z on y.a=z.a) WHERE x.a=1;
+a	a	a
+drop table t1,t2;

mysql-test/t/select.test

@@ -2015,3 +2015,13 @@ select a-b , (a-b < 0)  from t1 order by 1;
 select a-b as d, (a-b >= 0), b from t1 group by b having d >= 0;
 select cast((a - b) as unsigned) from t1 order by 1;
 drop table t1;
+
+#
+# Bug#8670
+#
+create table t1 (a int, b int);
+create table t2 like t1;
+select t1.a from (t1 inner join t2 on t1.a=t2.a) where t2.a=1;
+select t1.a from ((t1 inner join t2 on t1.a=t2.a)) where t2.a=1;
+select x.a, y.a, z.a from ( (t1 x inner join t2 y on x.a=y.a) inner join t2 z on y.a=z.a) WHERE x.a=1;
+drop table t1,t2;

sql/sql_parse.cc

@@ -5852,6 +5852,7 @@ TABLE_LIST *st_select_lex::end_nested_join(THD *thd)
 {
   TABLE_LIST *ptr;
   DBUG_ENTER("end_nested_join");
+  DBUG_ASSERT(embedding);
   ptr= embedding;
   join_list= ptr->join_list;
   embedding= ptr->embedding;
@@ -5865,6 +5866,12 @@ TABLE_LIST *st_select_lex::end_nested_join(THD *thd)
     join_list->push_front(embedded);
     ptr= embedded;
   }
+  else
+  if (nested_join->join_list.elements == 0)
+  {
+    join_list->pop();
+    DBUG_RETURN(0);
+  }
   DBUG_RETURN(ptr);
 }