sql - 如何在 SQL SELECT 语句中使用包常量？

Question

如何在 Oracle 的简单 SELECT 查询语句中使用包变量？

就像是

SELECT * FROM MyTable WHERE TypeId = MyPackage.MY_TYPE

是否有可能或仅在使用 PL/SQL 时(在 BEGIN/END 中使用 SELECT)？

Answer 1

你不能。

对于要在 SQL 语句中使用的公共(public)包变量，您必须编写一个包装函数以将值公开给外界:

SQL> create package my_constants_pkg
  2  as
  3    max_number constant number(2) := 42;
  4  end my_constants_pkg;
  5  /

Package created.

SQL> with t as
  2  ( select 10 x from dual union all
  3    select 50 from dual
  4  )
  5  select x
  6    from t
  7   where x < my_constants_pkg.max_number
  8  /
 where x < my_constants_pkg.max_number
           *
ERROR at line 7:
ORA-06553: PLS-221: 'MAX_NUMBER' is not a procedure or is undefined

创建一个包装函数:

SQL> create or replace package my_constants_pkg
  2  as
  3    function max_number return number;
  4  end my_constants_pkg;
  5  /

Package created.

SQL> create package body my_constants_pkg
  2  as
  3    cn_max_number constant number(2) := 42
  4    ;
  5    function max_number return number
  6    is
  7    begin
  8      return cn_max_number;
  9    end max_number
 10    ;
 11  end my_constants_pkg;
 12  /

Package body created.

现在它起作用了:

SQL> with t as
  2  ( select 10 x from dual union all
  3    select 50 from dual
  4  )
  5  select x
  6    from t
  7   where x < my_constants_pkg.max_number()
  8  /

         X
----------
        10

1 row selected.