表相關ddl：create/alter/drop table

基礎DDL語句包括：create table、alter table、drop table

• create table只會在標準庫中執行

• alter table、drop table要根據分片規則的設置在標準庫和對應的分片庫上執行

UDAL對數據庫建表DDL語句進行了擴展，支持設置分片規則。執行設置分片規則語句，dbproxy根據分片規則從標準庫獲取建表語句，再到對應的分片上執行。示例：

sharding @@table name='bill' set type='global' --設置全局表 
sharding @@table name='bill' set type='single' and dn='dn1' --設置單片表 
sharding @@table name='bill' set type='sharding' and sharding_func='mod-long-6' and sharding_id='sharding_id' and - sharding_area='sharding_area' and dn='dn1,dn2,dn3' --設置分片表(dn參數可選) 
sharding @@table name='bill' set type='inner' and inner_total='10' and inner_sharding_id='inner_sharding_id' and inner_sharding_func = 'inner_sharding_func' and dn='dn1' --設置單片表的庫內分表 
sharding @@table name='bill' set type='inner' and sharding_func='modlong-6' and sharding_id='sharding_id' and sharding_area='sharding_area' and inner_sharding_id='inner_sharding_id' and inner_sharding_func = 'inner_sharding_func' and dn='dn1,dn2,dn3' --設置分片表的庫內分表(dn參數可選)

支持create table和sharding合并為一條sql執行，即通過/* {sharding語句} */將sharding語句做為hint注釋，拼接到create table語句后面。使用示例如下：

CREATE TABLE IF NOT EXISTS `etasd9` (  `employee_id` int NOT NULL,  PRIMARY KEY (`employee_id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8/*sharding @@table name='etasd9' set type='sharding' and sharding_algo='PartitionByMod' and sharding_id='employee_id' and dn='asdadada_1,asdadada_2,asdadada_3,asdadada_4,asdadada_5'; */;