如何编写 PL/SQL 函数，该函数返回以函数参数为参数的 select 语句的结果？

Question

我尝试编写一个 PL/SQL 函数，其参数为表名和列名，它以表的形式返回查询结果。 这是我尝试过的：

CREATE TYPE TABLE_RES_OBJ AS OBJECT (
    employee_id number(30) ,
    person_id number(30),
    joined_year number(4), 
    salary number(20,2),
    qualification varchar2(45),
    department varchar2(45)
);
 /
create  TYPE table_ret as TABLE OF  table_res_obj;
 /
create or replace function select_custom(p_tablename varchar2, p_colname varchar2 ) return table_ret
is
    ret table_ret;
    query_txt varchar2(100) := 'SELECT :a from :b';
begin
    execute immediate query_txt bulk collect into ret using  p_colname, p_tablename;
        return ret;
end select_custom;

如您所见，这并不像想要的那样通用，但仍然无法正常工作，它说该表不存在，即使我尝试使用现有表运行它也是如此。

Answer 1

没错，它不会那样工作。您必须将表名和列名连接到 select 语句中。对于（简单）示例：

SQL> create or replace type table_res_obj as object
  2    (ename varchar2(20));
  3  /

Type created.

SQL> create or replace type table_ret as table of table_res_obj;
  2  /

Type created.

SQL> create or replace function select_custom
  2    (p_tablename varchar2, p_colname varchar2 )
  3  return table_ret
  4  is
  5    ret table_ret;
  6    query_txt varchar2(100);
  7  begin
  8    query_txt := 'select table_res_obj(' || dbms_assert.simple_sql_name(p_colname) ||') from ' ||
  9                  dbms_assert.sql_object_name(p_tablename);
 10    execute immediate query_txt bulk collect into ret;
 11    return ret;
 12  end select_custom;
 13  /

Function created.

有效吗？

SQL> select select_custom('dept', 'deptno') from dual;

SELECT_CUSTOM('DEPT','DEPTNO')(ENAME)
--------------------------------------------------------------------------------
TABLE_RET(TABLE_RES_OBJ('10'), TABLE_RES_OBJ('20'), TABLE_RES_OBJ('30'), TABLE_R
ES_OBJ('40'))


SQL>