从HGDB 1.3版本起，瀚高数据库引入了dual表，使得可以进行单行数据操作。例如，通过select语句展示版本信息或进行简单的数学运算。相比之下，PostgreSQL 9.6并不包含dual表，尝试在其中使用会返回错误。
从HGDB 1.3版本开始，瀚高数据库中添加了dual表：
highgo=# select version() from dual;
version
------------------------------------
HighGo Database 3.0.2 Linux 64-bit
(1 row)
highgo=# select version();
version
------------------------------------
HighGo Database 3.0.2 Linux 64-bit
(1 row)
highgo=#
highgo=# select 1+1 AAA from dual;
aaa
-----
2
(1 row)
highgo=# select 1+1 "AAA" from dual;
AAA
-----
2
(1 row)
highgo=# select 1+1 as "AAA" from dual;
AAA
-----
2
(1 row)
==============================
highgo=# select version() from dual;
version
------------------------------------
HighGo Database 3.0.2 Linux 64-bit
(1 row)
highgo=# select version();
version
------------------------------------
HighGo Database 3.0.2 Linux 64-bit
(1 row)
highgo=#
highgo=# select 1+1 AAA from dual;
aaa
-----
2
(1 row)
highgo=# select 1+1 "AAA" from dual;
AAA
-----
2
(1 row)
highgo=# select 1+1 as "AAA" from dual;
AAA
-----
2
(1 row)
==============================
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