How to make dynamic query using DBMS_SQL variable column names

Question

First of all i will show a working example of what i intend to do with "EXECUTE IMMEDIATE":
(EXECUTE IMMEDIATE has 32654 Bytes limit, which isn't enough for me so i'm exploring other methods such as DBMS_SQL)
-------------------------------------------------CODE-----------------------------------
create or replace PROCEDURE get_dinamic_query_content
(query_sql IN VARCHAR2, --any valid sql query ('SELECT name, age FROM table') 
list_fields IN VARCHAR2) --list of the columns name belonging to the query (  arr_list(1):='name';   arr_list(2):='age';
-- FOR k IN 1..arr_list.count LOOP
-- list_fields := list_fields || '||content.'||arr_list(k)||'||'||'''~cs~'''; )
AS
sql_stmt varchar (30000);
BEGIN
               sql_stmt :=
'DECLARE
     counter NUMBER:=0;     
auxcontent VARCHAR2(30000);     
     CURSOR content_cursor IS '|| query_sql ||';
     content content_cursor%rowtype;     
     Begin
          open content_cursor;
          loop
               fetch content_cursor into content;
               exit when content_cursor%notfound;
               begin                              
                    auxcontent := auxcontent || '||list_fields||';                    
               end;
               counter:=counter+1;     
          end loop;
          close content_cursor;
          htp.prn(auxcontent);
     END;';
EXECUTE IMMEDIATE sql_stmt;
END;
-------------------------------------------------CODE-----------------------------------
I'm attepting to use DBMS_SQL to perform similar instructions.
Is it possible?

Answer 1

Hi Pedro
You need to use DBMS_SQL here because you don't know how many columns your query is going to have before runtime. There are functions in DBMS_SQL to get information about the columns in your query - all this does is get the name.
SQL> CREATE OR REPLACE PROCEDURE get_query_cols(query_in IN VARCHAR2) AS
2 cur PLS_INTEGER;
3 numcols NUMBER;
4 col_desc_table dbms_sql.desc_tab;
5 BEGIN
6 cur := dbms_sql.open_cursor;
7 dbms_sql.parse(cur
8 ,query_in
9 ,dbms_sql.native);
10 dbms_sql.describe_columns(cur
11 ,numcols
12 ,col_desc_table);
13 FOR ix IN col_desc_table.FIRST .. col_desc_table.LAST LOOP
14 dbms_output.put_line('Column ' || ix || ' is ' ||
15 col_desc_table(ix).col_name);
16 END LOOP;
17 dbms_sql.close_cursor(cur);
18 END;
19 /
Procedure created.
SQL> exec get_query_cols('SELECT * FROM DUAL');
Column 1 is DUMMY
PL/SQL procedure successfully completed.
SQL> exec get_query_cols('SELECT table_name, num_rows FROM user_tables');
Column 1 is TABLE_NAME
Column 2 is NUM_ROWS
PL/SQL procedure successfully completed.
SQL> exec get_query_cols('SELECT column_name, data_type, low_value, high_value FROM user_tab_cols');
Column 1 is COLUMN_NAME
Column 2 is DATA_TYPE
Column 3 is LOW_VALUE
Column 4 is HIGH_VALUE
PL/SQL procedure successfully completed.I've just written this as a procedure that prints out the column names using dbms_output - I guess you're going to do something different with the result - maybe returning a collection, which you'll then parse through in Apex and print the output on the screen - this is just to illustrate the use of dbms_sql.
best regards
Andrew
UK