HGDB新版本开始兼容oracle varchar2类型，作用pg里的varchar类型支持一致
HGDB 1.3.1还不支持varchar2类型：
select version();
"HighGo Database 1.3.1 windows 64-bit"
create table test (name varchar2(10);
ERROR: syntax error at or near ";"
LINE 1: create table test (name varchar2(10);
^
********** 错误 **********
ERROR: syntax error at or near ";"
SQL 状态: 42601
字符:37
=============================================================================
HGDB 3.1.4开始支持varchar2类型：
highgo=# select version();
version
------------------------------------
HighGo Database 3.1.4 Linux 64-bit
(1 row)
highgo=# create table a (name varchar2(10));
CREATE TABLE
=============================================================================
PG 9.6.1不支持varchar2类型：
postgres9.6@[local]:5432 postgres# select version();
version
---------------------------------------------------------------------------------------------------------
PostgreSQL 9.6.1 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4), 64-bit
(1 row)
Time: 17.483 ms
postgres9.6@[local]:5432 postgres# create table a (name varchar2(10));
ERROR: type "varchar2" does not exist
LINE 1: create table a (name varchar2(10));
^
Time: 9.560 ms