Error in Looping with variable

Question

Dear All,
Please help me. i want to loop of record. i have two scheme. First, i make without variable and not error. Second, i make with variable and error occurs. as below my syntax:
First:
declare
x varchar(50);
begin
--x:='select dummy from dual';
for c1 in (select dummy from dual) loop
dbms_output.put_line(c1.dummy);
end loop;
end;
result:
X
Second:
declare
x varchar(50);
begin
x:='select dummy from dual';
for c1 in (x) loop
dbms_output.put_line(c1.dummy);
end loop;
end;
result:
Encountered the symbol 'LOOP' when expecting one...

Answer 1

Billy  Verreynne  wrote:
Why? For what purpose?
A cursor fetch loop is not the ideal processing structure.
It is slow. It requires data to travel from the buffer cache of the database into PL/SQL variables (in the PGA). It requires context switching between the PL/SQL and SQL engines.
It does not scale. More rows means more data to travel that path from the SQL engine to the PL/SQL engine. More loop iterations in PL/SQL. If a single loop iteration (for processing a row) is 1ms, then a 100,000 rows will take a 100 seconds. 200,000 rows 200 seconds. Etc. This clearly does not scale with an increase in data volume.
Also keep in mind that DBMS_OUTPUT does not write to screen or display anything. It is incapable of accessing a client device as it executes inside a server process. So each call to DBMS_OUTPUT stores that line of text in very expensive server memory. When the database call is done, the client (e.g. TOAD or SQL*Plus) can read those lines from the database and the client can display it.
So if your loop is for a 1000 rows, it means writing a 1000 lines of text into very expensive server memory - and then expecting the client to read that afterwards and display it. Why? This is not a standard client-server method. It also does not scale. It can actually crash the server when this method is abused.
The standard method would be to create a SQL cursor using PL/SQL code, and then return a reference handle (pointer) to the client. This allows the client the ability to fetch data directly from the cursor - in an optimal way that does not consume expensive server memory.I have to say it: I sincerely appreciate you taking the time to write this whenever it needs to be written rather than just giving up and letting people stumble along with bad design - it must take a lot of mental stamina to keep doing it. One day it will sink into my head also :-)