Getting results in a result set from dynamic SQL in Oracle

Question

This question is similar to a couple others I have found on StackOverflow, but the differences are signficant enough to me to warrant a new question, so here it is:

I want to obtain a result set from dynamic SQL in Oracle and then display it as a result set in a SqlDeveloper-like tool, just as if I had executed the dynamic SQL statement directly. This is straightforward in SQL Server, so to be concrete, here is an example from SQL Server that returns a result set in SQL Server Management Studio or Query Explorer:

EXEC sp_executesql N'select * from countries'

Or more properly:

DECLARE @stmt nvarchar(100)
SET @stmt = N'select * from countries'
EXEC sp_executesql @stmt

The question "How to return a resultset / cursor from a Oracle PL/SQL anonymous block that executes Dynamic SQL?" addresses the first half of the problem--executing dynamic SQL into a cursor. The question "How to make Oracle procedure return result sets" provides a similar answer. Web search has revealed many variations of the same theme, all addressing just the first half of my question. I found this post explaining how to do it in SqlDeveloper, but that uses a bit of functionality of SqlDeveloper. I am actually using a custom query tool so I need the solution to be self-contained in the SQL code. This custom query tool similarly does not have the capability to show output of print (dbms_output.put_line) statements; it only displays result sets. Here is yet one more possible avenue using 'execute immediate...bulk collect', but this example again renders the results with a loop of dbms_output.put_line statements. This link attempts to address the topic but the question never quite got answered there either.

Assuming this is possible, I will add one more condition: I would like to do this without having to define a function or procedure (due to limited DB permissions). That is, I would like to execute a self-contained PL/SQL block containing dynamic SQL and return a result set in SqlDeveloper or a similar tool.

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So to summarize:

• I want to execute an arbitrary SQL statement (hence dynamic SQL).
• The platform is Oracle.
• The solution must be a PL/SQL block with no procedures or functions.
• The output must be generated as a canonical result set; no print statements.
• The output must render as a result set in SqlDeveloper without using any SqlDeveloper special functionality.

Any suggestions?

Answer 1

Try try these.

DECLARE
  TYPE EmpCurTyp  IS REF CURSOR;
  v_emp_cursor    EmpCurTyp;
  emp_record      employees%ROWTYPE;
  v_stmt_str      VARCHAR2(200);
  v_e_job         employees.job%TYPE;
BEGIN
  -- Dynamic SQL statement with placeholder:
  v_stmt_str := 'SELECT * FROM employees WHERE job_id = :j';

  -- Open cursor & specify bind argument in USING clause:
  OPEN v_emp_cursor FOR v_stmt_str USING 'MANAGER';

  -- Fetch rows from result set one at a time:
  LOOP
    FETCH v_emp_cursor INTO emp_record;
    EXIT WHEN v_emp_cursor%NOTFOUND;
  END LOOP;

  -- Close cursor:
  CLOSE v_emp_cursor;
END;


declare
  v_rc    sys_refcursor;
begin
   v_rc := get_dept_emps(10);  -- This returns an open cursor
   dbms_output.put_line('Rows: '||v_rc%ROWCOUNT);
   close v_rc;
end;

Find more examples here. http://forums.oracle.com/forums/thread.jspa?threadID=886365&tstart=0

Answer 2

In TOAD when executing the script below you will be prompted for the type of v_result. From the pick list of types select cursor, the results are then displayed in Toad's data grid (the excel spreadsheet like result). That said, when working with cursors as results you should always write two programs (the client and the server). In this case 'TOAD' will be the client.

DECLARE
   v_result      sys_refcursor;
   v_dynamic_sql   VARCHAR2 (4000);
BEGIN
   v_dynamic_sql := 'SELECT * FROM user_objects where ' || ' 1 = 1';

   OPEN :v_result FOR (v_dynamic_sql);
END;

There may be a similar mechanism in Oracle's SQL Developer to prompt for the binding as well.

Answer 3

You seem to be asking for a chunk of PL/SQL code that will take an arbitrary query returning result set of undetermined structure and 'forward/restructure' that result set in some way such that is can easily be rendered by some "custom GUI tool".

If so, look into the DBMS_SQL for dynamic SQL. It has a DESCRIBE_COLUMNS procedure which returns the columns from a dynamic SELECT statement. The steps you would need are,

1. Parse the statement
2. Describe the result set (column names and data types)
3. Fetch each row, and for each column, call the datatype dependent function to return that value into a local variable
4. Place those local variables into a defined structure to return to the calling environment (eg consistent column names [such as col_1, col_2] probably all of VARCHAR2)

As an alternative, you could try building the query into an XMLFOREST statement, and parse the results out of the XML.

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Added : Unlike SQL Server, an Oracle PL/SQL call will not 'naturally' return a single result set. It can open up one or more ref cursors and pass them back to the client. It then becomes the client's responsibility to fetch records and columns from those ref cursors. If your client doesn't/can't deal with that, then you cannot use a PL/SQL call. A stored function can return a pre-defined collection type, which can allow you to do something like "select * from table(func_name('select * from countries'))". However the function cannot do DML (update/delete/insert/merge) because it blows away any concept of consistency for that query. Plus the structure being returned is fixed so that

select * from table(func_name('select * from countries'))

must return the same set of columns (column names and data types) as

select * from table(func_name('select * from persons'))

It is possible, using DBMS_SQL or XMLFOREST, for such a function to take a dynamic query and restructure it into a pre-defined set of columns (col_1, col_2, etc) so that it can be returned in a consistent manner. But I can't see what the point of it would be.