How to declare a cursor after BEGIN? - oracle

Question

I want to know if a cursor can be declared after BEGIN.
And how can I export the result of the plsql to an Excel sheet, because I have to run this procedure as a job.
CREATE OR REPLACE PROCEDURE masc(v_amsprogramid VARCHAR2) AS
v_mid VARCHAR2(50);
v_sid VARCHAR2(50);
CURSOR c1 IS
SELECT DISTINCT mid
FROM table_a WHERE aid = v_aid
ORDER BY mid;
BEGIN
OPEN c1;
LOOP
FETCH c1 INTO v_mid;
EXIT WHEN c1%NOTFOUND;
DECLARE
CURSOR c2 IS
SELECT DISTINCT sid INTO v_sid
FROM table_b WHERE mid = v_mid;
BEGIN
OPEN c2;
LOOP
FETCH c1 INTO v_mid;
EXIT WHEN c1%NOTFOUND;
dbms_output.PUT_LINE('MID : ' || v_mid);
dbms_output.PUT_LINE('Sid : ' || v_sid);
END LOOP;
CLOSE c2;
END LOOP;
CLOSE c1;
END masc;

Answer 1

I want to know if i can declare a cursor after begin
Not exactly. But you could use a cursor for loop instead of declaring an explicit cursor.
For example,
FOR i IN (SELECT distinct MID from table_a WHERE AID = V_AID ORDER BY MID)
LOOP
<do something>
END LOOP;
But anyway, this would be slower as row-by-row is slow-by-slow. I don't see a need of procedure at all. If you really need to do it in PL/SQL then consider BULK COLLECT.
And how can i export the result of the plsql to an excel sheet because i ahev to run this procedure as a job.
I don't see a need of PL/SQL in that case. You could simply use SPOOL in SQL*Plus.
For example,
sqlplus user/pass#service_name
<required formatting options>
SPOOL /location/myfile.csv
SELECT distinct MID from table_a WHERE AID = V_AID ORDER BY MID;
SPOOL OFF

Answer 2

Maybe you are looking for this:
create or replace PROCEDURE MASC (V_AMSPROGRAMID VARCHAR2) AS
V_MID VARCHAR2(50);
V_SID VARCHAR2(50);
CURSOR C1 IS
SELECT distinct MID from table_a WHERE AID = V_AID
ORDER BY MID;
CURSOR C2 IS
SELECT DISTINCT SID INTO V_SID FROM table_b WHERE MID = V_MID
ORDER BY MID;
BEGIN
...
or
create or replace PROCEDURE MASC (V_AMSPROGRAMID VARCHAR2) AS
V_MID VARCHAR2(50);
V_SID VARCHAR2(50);
CURSOR C1 IS
SELECT distinct MID from table_a WHERE AID = V_AID
ORDER BY MID;
CURSOR C2(v in NUMBER) IS
SELECT DISTINCT SID INTO V_SID FROM table_b WHERE MID = v
ORDER BY MID;
BEGIN
OPEN C1;
...
OPEN C2(V_MID);
...

Answer 3

U can use reference cursor for this purpose
create or replace PROCEDURE MASC (V_AMSPROGRAMID VARCHAR2) AS
V_MID VARCHAR2(50);
V_SID VARCHAR2(50);
C1 sys_refcursor ;
c2 sys_refcursor ;
BEGIN
OPEN C1 for SELECT distinct MID from table_a WHERE AID = V_AID
ORDER BY MID;
LOOP
FETCH C1 INTO V_MID;
EXIT WHEN C1%NOTFOUND;
open C2 for SELECT DISTINCT SID INTO V_SID FROM table_b WHERE MID = V_MID;
LOOP
FETCH C1 INTO V_MID;
EXIT WHEN C1%NOTFOUND;
DBMS_OUTPUT.PUT_LINE('MID : ' || V_MID);
DBMS_OUTPUT.PUT_LINE('Sid : ' || V_SID);
END LOOP;
CLOSE C2;
CLOSE C1;
END LOOP;

Answer 4

You can declare multiple cursors in the same pl/sql block. There is no need to declare the second cursor after you've opened the first cursor!
You would write something like:
create or replace procedure masc (p_amsprogramid varchar2)
as
v_mid varchar2(50);
v_sid varchar2(50);
cursor c1
is
select distinct mid
from table_a
where aid = p_amsprogramid
order by mid;
cursor c2
is
select distinct sid
from table_b
where mid = v_mid;
begin
open c1;
loop
fetch c1 into v_mid;
exit when c1%notfound;
open c2;
loop
fetch c1 into v_mid;
exit when c1%notfound;
dbms_output.put_line('mid : ' || v_mid);
dbms_output.put_line('sid : ' || v_sid);
end loop;
close c2;
end loop;
close c1;
end masc;
/
However, if you were to replace your open-cursor-loop-fetches as a cursor-for-loop, you could simplify things a bit:
create or replace procedure masc (p_amsprogramid varchar2)
as
cursor c1
is
select distinct mid
from table_a
where aid = p_amsprogramid
order by mid;
cursor c2
is
select distinct sid
from table_b
where mid = v_mid;
begin
for rec1 in c1
loop
for rec2 in c2
loop
dbms_output.put_line('mid : ' || rec1.mid);
dbms_output.put_line('sid : ' || rec2.sid);
end loop;
end loop;
end masc;
/
Looking at that, you've got a nested cursor loop. This screams procedural thinking, rather than set-based thinking, which is pretty much a big no-no when you're working with datasets in the database (ie. it's slow. You're having to constantly switch between the SQL and PL/SQL engines, instead of simply asking the SQL engine to calculate everything before delivering it to the PL/SQL engine).
By doing the nested cursor loop, you're basically reinventing NESTED LOOP joins - something the SQL engine can do far better than you can (not to mention it might not be the most efficient join, and the SQL engine could choose a better way of doing the join!). Any time you see a nested cursor loop, you should IMMEDIATELY stop and look to see if you can combine the queries into a single select statement. (Actually, any time you see a loop you should pause and consider whether you really do need it; sometimes it's necessary, but if you're doing something like selecting a set of results and then going through each row and then doing an update, consider merging the select into the update so that you have a statement that updates all the rows at once. It'll be much faster!)
For example, your original procedure could be rewritten as:
create or replace procedure masc (p_amsprogramid varchar2)
as
cursor c1
is
select distinct a.mid,
b.sid
from table_a a
inner join table_b b on (a.mid = b.mid)
where a.aid = p_amsprogramid
order by mid;
begin
for rec1 in c1
loop
dbms_output.put_line('mid : ' || rec1.mid);
dbms_output.put_line('sid : ' || rec1.sid);
end loop;
end masc;
/
Much simpler to read, understand and maintain, I think you'll agree!
If you're wanting to write the results of the sql query out as a file, you'll need to use UTL_FILE, instead of DBMS_OUTPUT. Bear in mind that the directory the file is written to needs to be something that is mounted/mapped to the server the database sits on. If you write the results as character-delimited, you can then easily import that file into Excel.
You might find this to be of use.