【标题】：Oracle 8i 中的union all不支持null
【关键字】：Oracle,8i,union,all,null
【来源】：http://blog.csdn.net/screend/archive/2006/12/19/1449551.aspx

Oracle 8i 中的union all不支持null

Oracle 9i 在8i的基础上对,union all 函数的改进.

以下是9i 数据库

SQL> select version from v$instance;

VERSION

-----------------

9.2.0.4.0

SQL> select 1 from dual

2 union all

3 select 2 from dual;

1

----------

1

2

SQL> select 1 from dual

2 union all

3 select null from dual;

1

----------

1

SQL> select sysdate from dual

2 union all

3 select null from dual;

SYSDATE

---------

19-DEC-06

以下是8i数据库.

SQL> select version from v$instance;

VERSION

-----------------

8.1.6.3.0

SQL> select 1 from dual

2 union all

3 select 2 from dual;

1

----------

1

2

SQL> select 1 from dual

2 union all

3 select null from dual;

select 1 from dual

*

ERROR at line 1:

ORA-01790: expression must have same datatype as corresponding expression

SQL> select 1 from dual

2 union

3 select null from dual;

select 1 from dual

*

ERROR at line 1:

ORA-01790: expression must have same datatype as corresponding expression

SQL> select sysdate from dual

2 union all

3 select sysdate from dual;

SYSDATE

---------

19-DEC-06

SQL> select sysdate from dual

2 union all

3 select null from dual;

select sysdate from dual

*

ERROR at line 1:

ORA-01790: expression must have same datatype as corresponding expression

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