ddl failed due to druid parser

[irene-coming]

• dble version：
  5.6.29-dble-9.9.9.9-78a278906811927e31ad0cdc0cc19c2379963992-20191012125722
• preconditions ：
  no
• configs：

schema.xml

rule.xml

server.xml

• steps：
  step1. query in dble

mysql> create table sharding_2_t1(id int, deleteAt int,username varchar(10),password char(10));
Query OK, 0 rows affected (0.36 sec)
mysql> alter table sharding_2_t1 add grade_id bigint default null,drop deleteAt, change username username varchar(50) default null, change password user_card_code varchar(50) default null;
ERROR 1064 (HY000): sql syntax error, no terminated. IDENTIFIER

• expect result：
  1.
• real result：
  1.
• supplements：
  1.bug is caused by druid parser, dble.log

2019-10-30 02:37:03.085  INFO [BusinessExecutor3] (com.actiontech.dble.route.impl.DefaultRouteStrategy.parserSQL(DefaultRouteStrategy.java:37)) - routeNormalSqlWithAST
com.alibaba.druid.sql.parser.ParserException: sql syntax error, no terminated. IDENTIFIER
        at com.alibaba.druid.sql.parser.SQLStatementParser.parseStatement(SQLStatementParser.java:2867) ~[druid-1.1.14.jar:1.1.14]
        at com.actiontech.dble.route.impl.DefaultRouteStrategy.parserSQL(DefaultRouteStrategy.java:35) [dble-2.19.03.1.jar:?]
        at com.actiontech.dble.route.impl.DefaultRouteStrategy.routeNormalSqlWithAST(DefaultRouteStrategy.java:73) [dble-2.19.03.1.jar:?]
        at com.actiontech.dble.route.impl.AbstractRouteStrategy.route(AbstractRouteStrategy.java:50) [dble-2.19.03.1.jar:?]
        at com.actiontech.dble.route.RouteService.route(RouteService.java:112) [dble-2.19.03.1.jar:?]
        at com.actiontech.dble.server.ServerConnection.routeEndExecuteSQL(ServerConnection.java:324) [dble-2.19.03.1.jar:?]
        at com.actiontech.dble.server.ServerConnection.execute(ServerConnection.java:267) [dble-2.19.03.1.jar:?]
        at com.actiontech.dble.server.ServerQueryHandler.query(ServerQueryHandler.java:166) [dble-2.19.03.1.jar:?]
        at com.actiontech.dble.net.FrontendConnection.query(FrontendConnection.java:330) [dble-2.19.03.1.jar:?]
        at com.actiontech.dble.net.FrontendConnection.query(FrontendConnection.java:346) [dble-2.19.03.1.jar:?]
        at com.actiontech.dble.net.handler.FrontendCommandHandler.handleData(FrontendCommandHandler.java:95) [dble-2.19.03.1.jar:?]
        at com.actiontech.dble.net.handler.FrontendCommandHandler.handle(FrontendCommandHandler.java:73) [dble-2.19.03.1.jar:?]
        at com.actiontech.dble.net.handler.FrontEndHandlerRunnable.run(FrontEndHandlerRunnable.java:44) [dble-2.19.03.1.jar:?]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [?:1.8.0_121]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [?:1.8.0_121]
        at java.lang.Thread.run(Thread.java:745) [?:1.8.0_121]