Please Request a Reasonable Conversion

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Here is something you need to be aware of when you use the EXECUTE IMMEDIATE … USING and OPEN FOR … USING statements in PL/SQL.

Let’s execute this simple anonymous PL/SQL block:

eddie@db11gr2> DECLARE
  2    l_string VARCHAR2 (4000);
  3    l_rc sys_refcursor;
  4  BEGIN
  5    l_string := RPAD (' ', 4000);
  6    OPEN l_rc FOR 'select :1 from dual' USING l_string;
  7    EXECUTE immediate 'select :1 from user_objects where rownum = 1'
  8      INTO l_string USING l_string;
  9  END;
 10  /

PL/SQL procedure successfully completed.

The EXECUTE IMMEDIATE and OPEN FOR statements are used with the USING clause. USING supplies a bind argument for the SQL string. In this example the value of the bind argument is a 4,000 character string.

Now, let’s pass a string greater than 4,000 characters to the OPEN FOR statement:

eddie@db11gr2> DECLARE
  2    l_string VARCHAR2 (4001);
  3    l_rc sys_refcursor;
  4  BEGIN
  5    l_string := RPAD (' ', 4001);
  6    OPEN l_rc FOR 'select :1 from dual' USING l_string;
  7  END;
  8  /
DECLARE
*
ERROR at line 1:
ORA-01460: unimplemented or unreasonable conversion requested
ORA-06512: at line 6

Oops, got an error. Let’s also try the EXECUTE IMMEDIATE statement with a string greater than 4,000 characters:

eddie@db11gr2> DECLARE
  2    l_string VARCHAR2 (4001);
  3  BEGIN
  4    l_string := RPAD (' ', 4001);
  5    EXECUTE immediate 'select :1 from user_objects where rownum = 1'
  6      INTO l_string USING l_string;
  7  END;
  8  /
DECLARE
*
ERROR at line 1:
ORA-01460: unimplemented or unreasonable conversion requested
ORA-06512: at line 5

Got the same error: “ORA-01460: unimplemented or unreasonable conversion requested”.

How about if we pass a NULL:

eddie@db11gr2> DECLARE
  2    l_rc sys_refcursor;
  3  BEGIN
  4    OPEN l_rc FOR 'select :1 from dual' USING NULL;
  5  END;
  6  /
  OPEN l_rc FOR 'select :1 from dual' USING NULL;
                                            *
ERROR at line 4:
ORA-06550: line 4, column 45:
PLS-00457: expressions have to be of SQL types
ORA-06550: line 4, column 3:

In this case we get “PLS-00457: expressions have to be of SQL types”.

Well, there is a restriction on what values you can bind: When binding values to dynamic SQL, only SQL datatypes are supported. You can bind strings, numbers, dates, collections, LOBs, XML documents… However, you cannot bind values having a PL/SQL specific datatype such as Booleans, associative arrays and varchar2 values greater than 4000.

Make sure you keep the above restriction in mind when you use the EXECUTE IMMEDIATE … USING and OPEN FOR … USING statements.

Source and resources:

• EXECUTE IMMEDIATE Statement
• Unsupported Data Type in Native Dynamic SQL
• OPEN FOR Statement
• Discussions about the ORA-01460 error

Related articles:

• More on Generating Strings
• CASE gotcha in Oracle 8i
• Here’s a Quick Way to Get the Line Number in PL/SQL

Filed in Oracle, Tips on 24 May 10 | Tags: pl/sql, sql

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