query with table alias as upper under [lower_case_tables_name=1] dble makes err explain

[irene-coming]

• dble version：
  5.6.29-dble-9.9.9.9-e3cf5f30028abdc697f92ca2de57efbb7f9b7a7f-20200102065411

• preconditions ：
  all backend mysql setting:
  lower_case_table_names=1

• configs：

schema.xml

<table name="sharding_2_t1" dataNode="dn1,dn2" cacheKey="id" rule="hash-two"/>

rule.xml

server.xml

• steps：
  step1. query in dble:

mysql> create table sharding_2_t1 (id int,busidate char(20),zoneno char(20),brno int,tellerno int) ;
Query OK, 0 rows affected (0.16 sec)
mysql> explain SELECT F.BUSIDATE, F.ZONENO, F.BRNO, F.TELLERNO FROM sharding_2_t1 F WHERE F.id = 1 UNION ALL SELECT '20180716', '00119', 1, 0 UNION ALL SELECT '20180716', '00119', 1, 2;
ERROR 1064 (HY000):  Table 'schema1.f' doesn't exist

mysql> explain SELECT f.BUSIDATE, f.ZONENO, f.BRNO, f.TELLERNO FROM sharding_2_t1 f WHERE f.id = 1 UNION ALL SELECT '20180716', '00119', 1, 0 UNION ALL SELECT '20180716', '00119', 1, 2;
+-----------+----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| DATA_NODE | TYPE     | SQL/REF                                                                                                                                                                   |
+-----------+----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| dn2       | BASE SQL | SELECT f.BUSIDATE, f.ZONENO, f.BRNO, f.TELLERNO FROM sharding_2_t1 f WHERE f.id = 1 UNION ALL SELECT '20180716', '00119', 1, 0 UNION ALL SELECT '20180716', '00119', 1, 2 |
+-----------+----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

• expect result：
  1.
  mysql> explain SELECT F.BUSIDATE, F.ZONENO, F.BRNO, F.TELLERNO FROM sharding_2_t1 F WHERE F.id = 1 UNION ALL SELECT '20180716', '00119', 1, 0 UNION ALL SELECT '20180716', '00119', 1, 2;
  +-----------+----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | DATA_NODE | TYPE | SQL/REF |
  +-----------+----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | dn2 | BASE SQL | SELECT f.BUSIDATE, f.ZONENO, f.BRNO, f.TELLERNO FROM sharding_2_t1 f WHERE f.id = 1 UNION ALL SELECT '20180716', '00119', 1, 0 UNION ALL SELECT '20180716', '00119', 1, 2 |
  +-----------+----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  1 row in set (0.00 sec)

• real result：
  1.

• supplements：
  1.dble expect table alias lower while user defined it upper

[wjl1619]

verified on version: 5.6.29-dble-2.19.11.0-3924537e81390ba76656e3c5071c194c7be7923b-20200210030705