Any EVAL() equalant functions in SQL or PL/SQL

Question

good day
i have 2 loops ,
outer loop has the real data from a table
and
inner loop has the column name to be selected from outer loop.
so in runtime, i need to select the columns dynamically .thats why i use inner loop. please see below.
for i in data Loop
for j in col_name Loop
--column name of data loop should be selected from this col_name loop.
dbms_output.put_line(i.||j.col_name);
End Loop;
End Loop;
But this should not work.
is there any eval function in plsql like in java and javascript to resolve this?
please advice.
thanks

Answer 1

> so in runtime, i need to select the columns dynamically .thats why i use
inner loop.
There are two basic approaches to dealing with dynamic projections. (projection = the columns and data types returned by a SELECT)
One is to use an interface that allows you, at run-time, to describe the projection. This is called a cursor's describe interface. In PL/SQL, that requires you to create a DBMS_SQL cursor. Details are in the [url
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14258/d_sql.htm#sthref7370]Oracle® Database PL/SQL Packages and Types Reference guide.
The other approach is to deal with the projection as a collection. This is illustrated below. The two problems with this approach is that you must use the collection's constructor in the projection, and that you must deal with implicit conversions or hardcode explicit data type conversions.
SQL> create or replace type TStrings as table of varchar2(4000);
2 /
Type created.
SQL>
SQL> declare
2 cursor c is
3 select
4 TStrings( object_id, object_name, object_type, created )
5 from user_objects
6 where rownum < 3;
7 colValue TStrings;
8 begin
9 open c;
10 loop -- data loop
11 fetch c into colValue;
12 DBMS_OUTPUT.put_line( '**start of row**' );
13 for i in 1..colValue.Count
14 loop -- column loop
15 DBMS_OUTPUT.put_line( 'column '||i||' value='|| colValue(i) );
16 end loop;
17 DBMS_OUTPUT.put_line( '**end of row**' );
18 exit when c%NOTFOUND;
19 end loop;
20 close c;
21* end;
SQL> /
**start of row**
column 1 value=12108
column 2 value=BIN$OU4aqY4cfvXgQPsKOl1I1A==$0
column 3 value=TABLE
column 4 value=2007/08/31 12:20:47
**end of row**
**start of row**
column 1 value=11753
column 2 value=BONUS
column 3 value=TABLE
column 4 value=2007/08/27 14:26:57
**end of row**
**start of row**
column 1 value=11753
column 2 value=BONUS
column 3 value=TABLE
column 4 value=2007/08/27 14:26:57
**end of row**
PL/SQL procedure successfully completed.
SQL>