"select *, select 3 from table_a" expect syntax error, but get resultset

[irene-coming]

• dble version： 5.6.29-dble-9.9.9.9-287a2f4-20180921052651
• preconditions ：
  no
• configs：

schema.xml

<table name="table_a" primaryKey="id" rule="hash-four" dataNode="dn1,dn2,dn3,dn4"></table>

• steps：
  step1. with dble and compare mysql execute sqls to prepare env:

create table table_a(id int, name varchar(20));
insert into table_a values(1,'a'),(2,'b');

step2.exeucte queries with mysql

mysql> select *,  select 3 from table_a limit 1;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'select 3 from table_a limit 1' at line 1

step3.execute queries with dble

mysql> select *,  select 3 from table_a limit 1;
+------------------+
| autoalias_scalar |
+------------------+
|                3 |
+------------------+
1 row in set (0.02 sec)

mysql> explain select *,  select 3 from table_a limit 1;
+--------------------+-----------------------+----------------------------------+
| DATA_NODE          | TYPE                  | SQL/REF                          |
+--------------------+-----------------------+----------------------------------+
| dn1_0              | BASE SQL              | select 1 from  `table_a` LIMIT 1 |
| dn2_0              | BASE SQL              | select 1 from  `table_a` LIMIT 1 |
| dn3_0              | BASE SQL              | select 1 from  `table_a` LIMIT 1 |
| dn4_0              | BASE SQL              | select 1 from  `table_a` LIMIT 1 |
| merge_1            | MERGE                 | dn1_0; dn2_0; dn3_0; dn4_0       |
| limit_1            | LIMIT                 | merge_1                          |
| shuffle_field_1    | SHUFFLE_FIELD         | limit_1                          |
| scalar_sub_query_1 | SCALAR_SUB_QUERY      | shuffle_field_1                  |
| dn1_1              | BASE SQL(May No Need) | scalar_sub_query_1; select 1     |
| merge_2            | MERGE                 | dn1_1                            |
| shuffle_field_2    | SHUFFLE_FIELD         | merge_2                          |
+--------------------+-----------------------+----------------------------------+
11 rows in set (0.00 sec)

• expect result：
  1.step3 get similar result with step2
• real result：
  1.dble with subquery without parenthesis between select and from get success
• supplements：
  1. dble's query plan seems a little strange.
  2. my real meant is to execute "select *, (select 3) from table_a limit 1;"

/label ~BUG

[sunsun314]

druid parser parse the sql as select *,(select 3 from table_a limit 1) ,the parse result is wrong.