Unfriendly tips for select * from sharding_1_t1 b,sharding_4_t1 c,(select * from sharding_2_t1) a on c.id=b.id and c.id=b.id

[FlyingMao]

• dble version：
  5.6.29-dble-9.9.9.9-3f3f64fa0c2733adccaa52b5bc652e1ea8725b56-20190311022855
• preconditions ：

create table sharding_1_t1(id int,name char);
create table sharding_2_t1(id int,name char);
create table sharding_4_t1(id int,name char);

• configs：

schema.xml

<schema name="schema1" sqlMaxLimit="100" dataNode="dn5">
        <table name="sharding_1_t1" primaryKey="id" dataNode="dn5" />
	<table name="sharding_2_t1" primaryKey="id" dataNode="dn1,dn2" rule="hash-two" />
        <table name="sharding_4_t1" dataNode="dn1,dn2,dn3,dn4" rule="hash-four" />
</schema>

rule.xml

server.xml

• steps：
  step1.

mysql> select * from sharding_1_t1 b,sharding_4_t1 c,(select * from sharding_2_t1) a on c.id=b.id and c.id=b.id;

• expect result：
  1.

mysql> select * from sharding_1_t1 b,sharding_4_t1 c,(select * from sharding_2_t1) a on c.id=b.id and c.id=b.id;
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 'on c.id=b.id and c.id=b.id' at line 1

• real result：
  1.

mysql> select * from sharding_1_t1 b,sharding_4_t1 c,(select * from sharding_2_t1) a on c.id=b.id and c.id=b.id;
ERROR 1066 (42000): Not unique table/alias: 'null'

• supplements：
  1.

/label ~BUG

[FlyingMao]

verified version： 5.6.29-dble-9.9.9.9-6d9aec3cbe94d2e217b42646dff266ecb7e5dfdb-20190318061530