Simple Stored Procedure for learning - oracle

Question

My journey is progressing and I'm learning rapidly. I can't get enough of this stuff... alas I am at a dead end here and need some help.
I am running Visual Studio, am connected to a database (that's filled with dummy data). I am able to run queries on it as expected. However, I'm learning about Procedures right now and I'm coming up with a problem.
I am trying to simply run a query that will select all from table.
CREATE PROCEDURE nearthetop()
BEGIN
SELECT * FROM RESULTS WHERE VOLUME = (SELECT MAX(VOLUME) FROM RESULTS WHERE VOLUME NOT In (SELECT Max(VOLUME) from RESULTS))
END;
When I run this inside Visual Studio I get an error:
EXECUTE FAIL:
CREATE PROCEDURE twofromtop() BEGIN SELECT * FROM RESULTS WHERE VOLUME = (SELECT MAX(VOLUME) FROM RESULTS WHERE VOLUME NOT In (SELECT Max(VOLUME) from RESULTS)) END
Message :
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'END' at line 3
When I remove BEGIN and END; from the procedure it creates it fine.
Why is that?
And then, once created, how do I "call" that procedure so as I can see the returned results?

Answer 1

In Oracle, when PL/SQL code uses a SELECT statement, you have to select into something - a local variable, a collection, whatever - or use a cursor loop and deal with cursor variable.
You're selecting row(s) whose volume value is the 2nd largest. Code you wrote works, but it fetches from the same table 3 times which isn't optimal. For example (based on Scott's sample schema), fetching the 2nd largest salary:
SQL> select ename, sal from emp order by sal desc;
ENAME SAL
---------- ----------
KING 5000 --> largest
FORD 3000 --> Ford and Scott both share
SCOTT 3000 --> the 2nd largest salary
JONES 2975
BLAKE 2850
CLARK 2450
<snip>
Your query returns correct result:
SQL> select *
2 from emp
3 where sal = (select max(sal) from emp
4 where sal not in (select max(sal) from emp)
5 );
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- -------- ---------- ---------- ----------
7788 SCOTT ANALYST 7566 09.12.82 3000 20
7902 FORD ANALYST 7566 03.12.81 3000 20
Consider doing it differently:
SQL> select *
2 from (select e.*,
3 rank() over (order by sal desc) rnk
4 from emp e
5 )
6 where rnk = 2;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO RNK
---------- ---------- --------- ---------- -------- ---------- ---------- ---------- ----------
7788 SCOTT ANALYST 7566 09.12.82 3000 20 2
7902 FORD ANALYST 7566 03.12.81 3000 20 2
SQL>
Now, back to your procedure. A simple option which doesn't require much effort is to use a cursor FOR loop. Procedure's IN parameter says which largest salary you want:
SQL> create or replace procedure nearthetop (par_n in number) as
2 begin
3 for cur_r in (select *
4 from (select e.*,
5 rank() over (order by sal desc) rnk
6 from emp e
7 )
8 where rnk = par_n
9 )
10 loop
11 dbms_output.put_line(cur_r.ename ||': '|| cur_r.sal);
12 end loop;
13 end;
14 /
Procedure created.
Testing:
SQL> set serveroutput on
SQL> begin
2 nearthetop(2); --> give me the 2nd largest salary
3 end;
4 /
SCOTT: 3000
FORD: 3000
PL/SQL procedure successfully completed.
SQL> begin
2 nearthetop(5); --> give me the 5th largest salary
3 end;
4 /
BLAKE: 2850
PL/SQL procedure successfully completed.
SQL>
I'm just displaying those values on the screen; you never said what you'd want to do with them.
If you'd like to return the result to the caller, a better option is to use a function instead of a procedure. In this case, it would be a ref cursor it returns.
SQL> create or replace function f_nearthetop (par_n in number)
2 return sys_refcursor
3 as
4 rc sys_refcursor;
5 begin
6 open rc for select *
7 from (select e.*,
8 rank() over (order by sal desc) rnk
9 from emp e
10 )
11 where rnk = par_n;
12 return rc;
13 end;
14 /
Function created.
Testing:
SQL> var l_rc refcursor
SQL>
SQL> exec :l_rc := f_nearthetop(2);
PL/SQL procedure successfully completed.
SQL> print :l_rc
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO RNK
---------- ---------- --------- ---------- -------- ---------- ---------- ---------- ----------
7788 SCOTT ANALYST 7566 09.12.82 3000 20 2
7902 FORD ANALYST 7566 03.12.81 3000 20 2
SQL>
So, yes - there are various options. Which one you'll actually use depends on what you want to do.
(As of Visual Studio: I can't help about it, I don't use it.)