How can we define output parameter size in stored procedure?

Question

How can we define output parameter size in stored procedure?

Answer 1

You can't. Of course, you are in control of how much data you put into the OUT parameter in the stored procedure. If you want you can create a sized local variable to hold the data and then assign the value of that variable to the OUT parameter.

The calling program determines the size of the variable that receives the OUT parameter.

Answer 2

Here is a simple package which declares and uses a subtype:

SQL> create or replace package my_pkg as
  2      subtype limited_string is varchar2(10);
  3      procedure pad_string (p_in_str varchar
  4                          , p_length number
  5                          , p_out_str out limited_string);
  6  end my_pkg;
  7  /

Package created.

SQL> create or replace package body my_pkg as
  2      procedure pad_string
  3          (p_in_str varchar
  4              , p_length number
  5              , p_out_str out limited_string)
  6      as
  7      begin
  8          p_out_str := rpad(p_in_str, p_length, 'A');
  9      end  pad_string;
 10  end my_pkg;
 11  /

Package body created.

SQL>

However, if we call PAD_STRING() in such a way that the output string exceeds the subtype's precision it still completes successfully. Bother!

SQL> var out_str varchar2(128)
SQL>
SQL> exec my_pkg.pad_string('PAD THIS!', 12, :out_str)

PL/SQL procedure successfully completed.

SQL>
SQL> select length(:out_str) from dual
  2  /

LENGTH(:OUT_STR)
----------------
              12

SQL>

This is annoying but it's the way PL/SQL works so we have to live with it.

The way to resolve the situaton is basically to apply DBC principles and validate our parameters. So, we can assert business rules against the inputs like this:

SQL> create or replace package body my_pkg as
  2      procedure pad_string
  3          (p_in_str varchar
  4              , p_length number
  5              , p_out_str out limited_string)
  6      as
  7      begin
  8          if length(p_in_str) + p_length > 10 then
  9              raise_application_error(
 10                      -20000
 11                      , 'Returned string cannot be longer than 10 characters!');
 12          end if;
 13          p_out_str := rpad(p_in_str, p_length, 'A');
 14      end  pad_string;
 15  end my_pkg;
 16  /

Package body created.

SQL>
SQL> exec my_pkg.pad_string('PAD THIS!', 12, :out_str)
BEGIN my_pkg.pad_string('PAD THIS!', 12, :out_str); END;

*
ERROR at line 1:
ORA-20000: Returned string cannot be longer than 10 characters!
ORA-06512: at "APC.MY_PKG", line 9
ORA-06512: at line 1


SQL>

Or we can assert business rules against the output like this:

SQL> create or replace package body my_pkg as
  2      procedure pad_string
  3          (p_in_str varchar
  4              , p_length number
  5              , p_out_str out limited_string)
  6      as
  7          l_str limited_string;
  8      begin
  9          l_str := rpad(p_in_str, p_length, 'A');
 10          p_out_str := l_str;
 11      end  pad_string;
 12  end my_pkg;
 13  /

Package body created.

SQL>
SQL> exec my_pkg.pad_string('PAD THIS!', 12, :out_str)
BEGIN my_pkg.pad_string('PAD THIS!', 12, :out_str); END;

*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at "APC.MY_PKG", line 9
ORA-06512: at line 1

SQL>

In most scenarios we should do both. This is the polite way to build interfaces, because it means other routines can call our procedures with the confidence that they will return the values they say they will.