table's order in complex query with multi-table is rand

[irene-coming]

• dble version：
  5.6.29-dble-9.9.9.9-3bc0fd1498a4e28065918507d64ee63ca440d386-20200210030514

• preconditions ：
  no

• configs：

schema.xml

<schema name="schema1" sqlMaxLimit="100" dataNode="dn5">
    <table name="sharding_two_node" dataNode="dn1,dn2" rule="hash-two"/>
    <table name="sharding_two_node2" dataNode="dn1,dn2" rule="hash-two"/>
</schema>

rule.xml

server.xml

• steps：
  step1. prepare data in dble

CREATE TABLE `sharding_two_node` (
  `id` int(11) DEFAULT NULL,
  `c_flag` int(11) DEFAULT NULL,
  `c_decimal` float DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE `sharding_two_node2` (   `id` int(11) DEFAULT NULL,   `c_flag` int(11) DEFAULT NULL,   `c_decimal` float DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1;
insert into sharding_two_node values(2,2,2);
insert into sharding_two_node2 values(2,2,2);

    step2. get explain of sql:
```mysql
explain select b.*,a.* from sharding_two_node a join sharding_two_node2 b where a.id =b.id and (a.c_decimal=1 or (( a.id =1 and b.id=1) or ( a.c_flag=b.c_flag and a.id =2 ))) \G
*************************** 1. row ***************************
DATA_NODE: dn1_0
     TYPE: BASE SQL
  SQL/REF: select `a`.`id`,`a`.`c_flag`,`a`.`c_decimal`,`b`.`id`,`b`.`c_flag`,`b`.`c_decimal` from  `sharding_two_node` `a` join  `sharding_two_node2` `b` on `a`.`id` = `b`.`id` where ((`a`.`id` = 1) OR (`a`.`id` = 2) OR (a.c_decimal IN (1))) AND (((`a`.`id` = 1) AND (`b`.`id` = 1)) OR ((`a`.`c_flag` = `b`.`c_flag`) AND (`a`.`id` = 2)) OR (a.c_decimal IN (1)))
*************************** 2. row ***************************
DATA_NODE: dn2_0
     TYPE: BASE SQL
  SQL/REF: select `a`.`id`,`a`.`c_flag`,`a`.`c_decimal`,`b`.`id`,`b`.`c_flag`,`b`.`c_decimal` from  `sharding_two_node` `a` join  `sharding_two_node2` `b` on `a`.`id` = `b`.`id` where ((`a`.`id` = 1) OR (`a`.`id` = 2) OR (a.c_decimal IN (1))) AND (((`a`.`id` = 1) AND (`b`.`id` = 1)) OR ((`a`.`c_flag` = `b`.`c_flag`) AND (`a`.`id` = 2)) OR (a.c_decimal IN (1)))
*************************** 3. row ***************************
DATA_NODE: merge_1
     TYPE: MERGE
  SQL/REF: dn1_0; dn2_0
*************************** 4. row ***************************
DATA_NODE: shuffle_field_1
     TYPE: SHUFFLE_FIELD
  SQL/REF: merge_1
4 rows in set (0.01 sec)

• expect result：
  in result of explain, the order of table a and b are valid
• real result：
  1. in step2,
     *************************** 1. row ***************************
     DATA_NODE: dn1_0
     TYPE: BASE SQL
     SQL/REF: select a.id,a.c_flag,a.c_decimal,b.id,b.c_flag,b.c_decimal from sharding_two_node a join sharding_two_node2 b on a.id = b.id where ((a.id = 1) OR (a.id = 2) OR (a.c_decimal IN (1))) AND (((a.id = 1) AND (b.id = 1)) OR ((a.c_flag = b.c_flag) AND (a.id = 2)) OR (a.c_decimal IN (1)))

select a.id,a.c_flag,a.c_decimal,b.id,b.c_flag,b.c_decimal from ...
is odds, some times it's:
select b.id,b.c_flag,b.c_decimal,a.id,a.c_flag,a.c_decimal from ...

• supplements：
  1.

[wjl1619]

verified on version: 5.6.29-dble-2.19.11.0-a8b6cf2daf30fd1dedb6e91294d8b6839e730386-20200211092945