想送点分给大家

这里还有个小小的疑问:
在PostgreSQL数据库中我没发现有varchar类型。但是能使用varchar建表。是怎么回事？CREATE TABLE test(
    id INT NOT NULL ,
    title VARCHAR (100) NOT NULL,
    auther VARCHAR(50),
    sentence VARCHAR(1000) NOT NULL
); 
这样建表成功了的。在系统数据里postgres中有个pg_type的系统表.我在这个表里找不到varchar类型只找到一个_varchar这个类型。前面多了个下划线！下面是对postgresql支持的所有类型：
我很疑惑：望解答......
peek=> \i ./select.sql
              typname              | typtype | typcategory | typdelim | typalign 
-----------------------------------+---------+-------------+----------+----------
 bool                              | b       | B           | ,        | c
 bytea                             | b       | U           | ,        | i
 char                              | b       | S           | ,        | c
 name                              | b       | S           | ,        | c
 int8                              | b       | N           | ,        | d
 int2                              | b       | N           | ,        | s
 int2vector                        | b       | A           | ,        | i
 int4                              | b       | N           | ,        | i
 regproc                           | b       | N           | ,        | i
 text                              | b       | S           | ,        | i
 oid                               | b       | N           | ,        | i
 tid                               | b       | U           | ,        | s
 xid                               | b       | U           | ,        | i
 cid                               | b       | U           | ,        | i
 oidvector                         | b       | A           | ,        | i
 pg_type                           | c       | C           | ,        | d
 pg_attribute                      | c       | C           | ,        | d
 pg_proc                           | c       | C           | ,        | d
 pg_class                          | c       | C           | ,        | d
 xml                               | b       | U           | ,        | i
 _xml                              | b       | A           | ,        | i
 smgr                              | b       | U           | ,        | s
 point                             | b       | G           | ,        | d
 lseg                              | b       | G           | ,        | d
 path                              | b       | G           | ,        | d
 box                               | b       | G           | ;        | d
 polygon                           | b       | G           | ,        | d
 line                              | b       | G           | ,        | d
 _line                             | b       | A           | ,        | d
 float4                            | b       | N           | ,        | i
 float8                            | b       | N           | ,        | d
 abstime                           | b       | D           | ,        | i
 reltime                           | b       | T           | ,        | i
 tinterval                         | b       | T           | ,        | i
 unknown                           | b       | X           | ,        | c
 circle                            | b       | G           | ,        | d
 _circle                           | b       | A           | ,        | d
 money                             | b       | N           | ,        | d
 _money                            | b       | A           | ,        | d
 macaddr                           | b       | U           | ,        | i
 inet                              | b       | I           | ,        | i
 cidr                              | b       | I           | ,        | i
 _bool                             | b       | A           | ,        | i
 _bytea                            | b       | A           | ,        | i
 _char                             | b       | A           | ,        | i
 _name                             | b       | A           | ,        | i
 _int2                             | b       | A           | ,        | i
 _int2vector                       | b       | A           | ,        | i
 _int4                             | b       | A           | ,        | i
 _regproc                          | b       | A           | ,        | i
 _text                             | b       | A           | ,        | i
 _oid                              | b       | A           | ,        | i
 _tid                              | b       | A           | ,        | i
 _xid                              | b       | A           | ,        | i
 _cid                              | b       | A           | ,        | i
 _oidvector                        | b       | A           | ,        | i
 _bpchar                           | b       | A           | ,        | i
 _varchar                          | b       | A           | ,        | i
 _int8                             | b       | A           | ,        | d
 _point                            | b       | A           | ,        | d
 _lseg                             | b       | A           | ,        | d
 _path                             | b       | A           | ,        | d
 _box                              | b       | A           | ;        | d
 _float4                           | b       | A           | ,        | i
 _float8                           | b       | A           | ,        | d
 .........