Allow users to SELECT from dynamic SQL - oracle

Question

I've been looking at the DBMS_SQL package in Oracle and trying to see if there is a way to create a view or something that users can select from to see the results of a dynamic SQL query.
I have a test procedure based on the documentation:
CREATE OR REPLACE PROCEDURE test_dyn_sql AS
cursor_name INTEGER;
rows_processed INTEGER;
l_query LONG;
BEGIN
l_query := 'SELECT SYSDATE AS the_date, ''ABC'' AS the_string, 1 AS the_int FROM dual';
cursor_name := dbms_sql.open_cursor;
DBMS_SQL.PARSE(cursor_name, l_query, DBMS_SQL.NATIVE);
rows_processed := DBMS_SQL.EXECUTE(cursor_name);
DBMS_SQL.CLOSE_CURSOR(cursor_name);
EXCEPTION
WHEN OTHERS THEN
DBMS_SQL.CLOSE_CURSOR(cursor_name);
DBMS_OUTPUT.put_line('ERROR');
END;
But this just executes the statement and does not return anything. What I'd like is a view so a user can just do a SELECT the_date FROM some_view and get the results. I will not know the names or number of columns in advance, so that's why I'm after a dynamic SQL solution.

Answer 1

" I will not know the names or number of columns in advance, so that's
why I'm after a dynamic SQL solution"
That's pretty hard to implement in SQL: SQL is all about the data structures, and it really expects the columns to exist up front. So you cannot build a VIEW on a mutable data structure.
You can implement a function which returns a ref cursor. This is a pointer to a data structure which can be interpreted by a client, say as a JDBC ResultSet.
Here's an example function which takes a table name and column name, assembles the query and returns its result set.
CREATE OR REPLACE FUNCTION test_dyn_sql
(tab_name in varchar2
, col_name in varchar2)
return sys_refcursor
AS
return_value sys_refcursor;
BEGIN
open return_value for
'SELECT SYSDATE AS the_date, '||col_name||' FROM '||tab_name;
return return_value;
END;
/
The output is not very elegant in SQL*Plus but you get the idea.
SQL> select test_dyn_sql ('EMP', 'NAME') from dual;
TEST_DYN_SQL('EMP','
--------------------
CURSOR STATEMENT : 1
CURSOR STATEMENT : 1
THE_DATE NAME
--------- ------------------------------
03-APR-15 FOX IN SOCKS
03-APR-15 MR KNOX
03-APR-15 DAISY-HEAD MAYZIE
SQL>
I suggest you stick with Native Dynamic SQL (that is, execute immediate) as much as possible: as you can see, it's really simple compared to DBMS_SQL. Only reach for DBMS_SQL when you have some extremely complicated requirement.
I appreciate this may not be the solution form you're looking for. If that is the case please edit your question to provide more details about the problem you're trying to solve.

Answer 2

If you want your code to return the value of rows_processed variable use the code below which will return 0.
CREATE OR REPLACE FUNCTION test_dyn_sql(asd INTEGER) RETURN INTEGER AS
cursor_name INTEGER;
rows_processed INTEGER;
l_query LONG;
BEGIN
l_query := 'SELECT SYSDATE AS the_date, ''ABC'' AS the_string, 1 AS the_int FROM dual';
cursor_name := dbms_sql.open_cursor;
DBMS_SQL.PARSE(cursor_name, l_query, DBMS_SQL.NATIVE);
rows_processed := DBMS_SQL.EXECUTE(cursor_name);
DBMS_SQL.CLOSE_CURSOR(cursor_name);
RETURN rows_processed;
EXCEPTION
WHEN OTHERS THEN
DBMS_SQL.CLOSE_CURSOR(cursor_name);
DBMS_OUTPUT.put_line('ERROR');
RETURN 0;
END;
This is how you call the function from plsql
DECLARE
rows_precessed INTEGER;
BEGIN
rows_precessed := test_dyn_sqll(0);
DBMS_OUTPUT.put_line(rows_precessed);
END;