Oracle – Invoking a function call in a string in an Oracle Procedure


I writing an application using Oracle 10g.

I am currently facing this problem. I take in "filename" as parameter of type varchar2.

A sample value that filename may contain is: 'TEST || to_char(sysdate, 'DDD')'.

In the procedure, I want to get the value of this file name as in TEST147.
When i write:

select filename
into ffilename
from dual;

I get the value ffilename = TEST || to_char(sysdate, 'DDD') whick makes sense. But how can I get around this issue and invoke the function in the string value?

Help appreciated.

Best Solution

It's easy enough to dynamically execute a string ...

create or replace function fmt_fname (p_dyn_string in varchar2)
    return varchar2
    return_value varchar2(128);
    execute immediate 'select '||p_dyn_string||' from dual'
        into return_value;
    return  return_value;
end fmt_fname;

The problem arises where your string contains literals, with the dreaded quotes ...

SQL> select fmt_fname('TEST||to_char(sysdate, 'DDD')') from dual
  2  /
select fmt_fname('TEST||to_char(sysdate, 'DDD')') from dual
ERROR at line 1:
ORA-00907: missing right parenthesis


So we have to escape the apostrophes, all of them, including the ones you haven't included in your posted string:

SQL> select * from t34
  2  /

---------- ------------------------------
         1 APC001
         2 XYZ213
         3 TEST147

SQL> select * from t34
  2  where filename = fmt_fname('''TEST''||to_char(sysdate, ''DDD'')')
  3  /

---------- ------------------------------
         3 TEST147



Just for the sake of fairness I feel I should point out that Tony's solution works just as well:

SQL> create or replace function fmt_fname (p_dyn_string in varchar2)
  2      return varchar2
  3  is
  4      return_value varchar2(128);
  5  begin
  6      execute immediate 'begin :result := ' || p_dyn_string || '; end;'
  7          using out return_value;
  8      return  return_value;
  9  end;
 10  /

Function created.

SQL> select fmt_fname('''TEST''||to_char(sysdate, ''DDD'')') from dual
  2  /



In fact, by avoiding the SELECT on DUAL it is probably better.

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