Oracle iteration and collections - oracle

Question

How I can iterate over loop and collect information inside variable/collection?
Something like:
cursor cursor_c= select col1 from table1 where condition;
collection l;
foreach row in cursor_c
l.add (select col2 from table2 where col1=row);
end;
printout(l);
I want to run this as script not inside a procedure.
I have 0 experience with PL/SQL so any help will be appreciated!

Answer 1

You can duplicate the logic shown, but except in unusual circumstances I wouldn't recommend doing it that way. Collections are available and useful in PL/SQL, but printing them out is done by looping over the collection - so if all you're doing is collecting something in-memory to print it out, the better choice would be simply to print the items coming from the cursor when the cursor is iterated. In addition, doing a singleton SELECT inside a loop, where the data being selected in the inner SELECT is dependent on the outer SELECT, is equivalent to doing a JOIN - so do the join instead of pinging the database with a bunch of single-row SELECTs. Putting this together I suggest doing something like:
BEGIN
FOR aRow in (SELECT t2.COL2
FROM TABLE1 t1
INNER JOIN TABLE2 t2
ON t2.COL1 = t1.COL1
WHERE t1.WHATEVER = vSOMETHING_ELSE)
LOOP
DBMS_OUTPUT.PUT_LINE(aRow.COL2);
END LOOP;
END;
In PL/SQL the best choice is generally to use a cursor to get the data in the form you want it, rather than collecting data and then iterating over the collection to transform it. Your data resides in the database - learn to work with it there.
Best of luck.

Answer 2

If you simply want a column in a table matching a column from another table, you won't need a loop, simply use JOINS
SELECT t2.col2
FROM table1 t1
JOIN table2 t2 ON t2.col1 = t1.col1
WHERE '<your_where_conditon>'
If you do want to display them using dbms_output, you may simply use an implicit cursor loop ( #Bob Jarvis answer) or BULK COLLECT to load into a collection.
DECLARE
TYPE col2type is TABLE OF table2.col2%TYPE;
col2_t col2type;
BEGIN
SELECT t2.col2 BULK COLLECT INTO col2_t
FROM table1 t1
INNER JOIN table2 t2 ON t2.col1 = t1.col1
WHERE '<your_where_conditon>';
for i in 1..col2_t.count
loop
dbms_output.put_line(col2_t(i).col2);
end loop;
END;
/

Answer 3

Below code snippet will solve your problem.
set serveroutput on;
declare
type ty_tb_name is table of varchar2(20) index by pls_integer;
l_tb_name ty_tb_name;
cursor cur_acc_name is
select account_name from cust_account;
idx number := 1;
begin
for rec in cur_acc_name loop
l_tb_name(idx) := rec.account_name;
idx := idx+1;
exit when cur_acc_name%notfound;
end loop;
DBMS_OUTPUT.put_line('count:'||l_tb_name.count);
for i in l_tb_name.first..l_tb_name.count loop
DBMS_OUTPUT.put_line('name:'||l_tb_name(i));
end loop;
exception
when others then
DBMS_OUTPUT.put_line(SQLERRM);
end;
/