Using dynamic value in procedure on column

Question

I want a PL/sql procedure to select the data from the column dynamically into a variable .
My friend suggested its not possible in PL/sql ,its only possible in sql .
What i want is when i execute the PL/sql procedure the a_1 must get the value of the data in the table,i do not want to use execute immediate in pl/sql.
I create a table A
create table A (a1 number,a2 number,a3 number);
insert into a values (1,2,3);
then i create a procedure
create or replace
procedure test_a (var IN number)
as
a_1 number;
i number;
z varchar2(5);
begin
if var=1
then
i:=1;
elsif var = 2
then
i:=2;
z:='A2';
end if;
SELECT 'a'||i into a_1 from a;
end;
Edited by: user536416 on May 13, 2010 4:03 AM

Answer 1

I prefer reference cursors over execute immediate if I must do dynamic SQL (and have learned not to do it unless necessary - among other things dynamic SQL is hard to debug and maintain).
The advantages to ref cursors are
* execute immedate will only retrieve one row, ref cursors as many as you want
* easier for me to build the query first, then execute it (though you can do this with execute immediate too) for debugging
You can buiid the query dynamcially but have to be careful to make sure the select list matches the INTO clause on the fetch statements. Although the queries in the example below are hard coded I could have done something like
  v_command_c := 'select '||var1||', '||var2||' from '''||table_name||'''';
  open refcur for v_command_c;To randomize your column selection use something like the above with IF logic and a randomizer, possibly the DBMS_RANDOM package or a time extraction.
Something like
SET SCAN OFF
SET SERVEROUTPUT ON
DECLARE
  --define composite data types
  --reference cursor type - structure
  TYPE RefCursorType   IS REF CURSOR;
  --collection (index-by table) type - structure
  TYPE TablesTableType IS TABLE OF user_tables.table_name%TYPE
    INDEX BY BINARY_INTEGER;
  --define ref cursors to be used in BEGIN section
  UserTablesCursor RefCursorType;
  UserViewCursor   RefCursorType;
  --define actual index-by tables to be used in BEGIN section
  NamesTable TablesTableType;
  ViewsTable TablesTableType;
  --define internal procedures to be used in this script
  PROCEDURE ListItems(RefCursor IN RefCursorType,
    DataTable IN OUT TablesTableType
    ) IS
    Counter   INTEGER := 1;
    TableName user_tables.table_name%TYPE;
  BEGIN
    FETCH RefCursor INTO DataTable(Counter);
    Counter := Counter + 1;
    WHILE RefCursor%FOUND LOOP
      FETCH RefCursor INTO DataTable(Counter);
      Counter := Counter + 1;
    END LOOP;
  END; --ListItems;
  PROCEDURE WriteItems(DataTable IN TablesTableType) IS
  BEGIN
    FOR i IN 1..DataTable.count LOOP
      dbms_output.put_line(DataTable(i));
    END LOOP;
  END; --WriteItems;
BEGIN
  OPEN UserTablesCursor FOR
    SELECT table_name
      FROM user_tables;
  ListItems(UserTablesCursor,NamesTable);
  CLOSE UserTablesCursor;
  dbms_output.put_line('user_tables');
  dbms_output.put_line('--------------');
  WriteItems(NamesTable);
  --second defintion & set of calls
  dbms_output.put_Line(CHR(13));
  OPEN UserTablesCursor FOR
    SELECT view_name
      FROM user_views;
  ListItems(UserTablesCursor,ViewsTable);
  CLOSE UserTablesCursor;
  dbms_output.put_line('user_views');
  dbms_output.put_line('--------------');
  WriteItems(ViewsTable);
END;
/Edited by: riedelme on May 13, 2010 5:44 AM