Using variables to specify tables and columns in a function

Question

All,
I'm trying to create a function to select a random table, random column, random row, and return the data. I'm not quite sure how to use the table_name once I have it stored in the variable and I'm hoping someone can help.
Here is the code:
create or replace function sknddstr (asdf in varchar2)
return varchar2
is
v_table      varchar2(50);
v_column      varchar2(50);
v_data           varchar2(50);
v_return      varchar2(160);
begin
select     asdf.table_name into v_table
from     dual
,     (select     table_name
     from     user_tables
     where     table_name not like 'TEMP%'
     order by      dbms_random.random) asdf
where     rownum < 2;
select fdsa.column_name into v_column
from     dual
,     (select column_name
     from     user_tab_cols
     where     table_name = v_table
     and     nullable = 'Y'
     order by     dbms_random.random) fdsa
where     rownum < 2;
select     v_column into v_data
from     dual
,     (select v_column
     from     v_table
     order by dbms_random.random)
where     rownum < 2;
select v_table || ' | ' || v_column || ' | ' || v_data into v_return
from dual;
return v_return;
end;
Any suggestions? BTW, I know I don't use the IN asdf, but I'm not sure how to create a function with no parameters.
Thanks again!

Answer 1

You need to use dynamic SQL whenever you substitute object names (table, column, etc.) at runtime. I would suggest something like (note I have changed the filters to match my data):
sql>create or replace function f_random_data
  2    return varchar2
  3  is
  4    v_table_name   user_tab_columns.table_name%type;
  5    v_column_name  user_tab_columns.column_name%type;
  6    v_data         varchar2(4000);
  7  begin
  8    select table_name, column_name
  9      into v_table_name, v_column_name
10      from (select table_name, column_name
11              from user_tab_columns
12             where table_name = (select table_name
13                                   from (select table_name
14                                           from user_tables
15                                          where table_name in ('EMP', 'DEPT')
16                                          order by dbms_random.random)
17                                  where rownum <= 1)
18  --             and nullable = 'Y'                  
19             order by dbms_random.random)
20     where rownum <= 1;                                
21 
22    execute immediate
23      'select *' ||
24      '  from (select ' || v_column_name ||
25              '  from ' || v_table_name ||
26              ' order by dbms_random.random)' ||
27      ' where rownum <= 1'
28      into v_data;
29 
30    return (v_table_name || '|' || v_column_name || '|' || v_data);
31  end;
32  /
Function created.
sql>select f_random_data from dual;
F_RANDOM_DATA
EMP|COMM|500
1 row selected.
sql>/
F_RANDOM_DATA
DEPT|DNAME|SALES
1 row selected.
sql>/
F_RANDOM_DATA
DEPT|DEPTNO|40
1 row selected.
sql>/
F_RANDOM_DATA
EMP|ENAME|SCOTT
1 row selected.
sql>/
F_RANDOM_DATA
DEPT|DNAME|OPERATIONS
1 row selected.