Compilation errors with store procedure

Question

Hi guys, I just started SQL so forgive me if I ask any real stupid questions. This is the problem I have right now as said in my title.
This is my procedure.sql
CREATE OR REPLACE PROCEDURE verify IS
no_of_duplicates NUMBER:=0;
BEGIN
SELECT COUNT(*) INTO no_of_duplicates
FROM EMPLOYEE
WHERE E# =
(sELECT E# FROM DRIVER
WHERE EXISTS
(SELECT E# FROM MECHANIC
WHERE DRIVER.L# = MECHANIC.L#));
IF no_of_duplicates:=0 THEN dbms_output.put_line('OK');
ELSE
SELECT E#,NAME FROM EMPLOYEE
WHERE E# =
(SELECT E# FROM DRIVER
WHERE EXISTS
(SELECT E# FROM MECHANIC
WHERE DRIVER.L# = MECHANIC.L#));
END IF;
END verify;
While trying to create the procedure, it gives me the compilation errors. I have been stuck with this for hours and can't seem to find anything wrong with it. Can anyone point me in the right direction? Thanks!

Answer 1

Hi,
Once again, post your code.  The error occurs when you call the procedure, but you haven't posted the code that calls the procedure and causes the error.
When I do this in SQL*Plus:
SET  SERVEROUTPUT  ON  FORMAT WRAPPED
EXEC  verify;
The procedure you posted runs perfectly (that is, is displays the e# only, exactly as it was designed to do).
One way to display both the e# and the name is to BULK COLLECT both the e# and name into separate collections, like this:
CREATE OR REPLACE PROCEDURE verify IS 
    TYPE  e#_table  IS TABLE OF employee.e#%TYPE;
    e#_list    e#_table;
    TYPE  name_table  IS TABLE OF employee.name%TYPE;
    name_list  name_table;
BEGIN 
    SELECT            e#,       name
    BULK COLLECT INTO e#_list,  name_list
    FROM              employee 
    WHERE   e# IN (
                      SELECT  d.e#
                      FROM    driver    d
                      JOIN    mechanic  m  ON  d.e#  = m.e# 
    IF  e#_list.COUNT  = 0
    THEN
        dbms_output.put_line ('OK, there are no illict duplications');
    ELSE     -- that is, e#_list.COUNT <> 0
        dbms_output.put_line ('The following employees are both drivers and mechanics:');
        FOR j IN 1..e#_list.COUNT LOOP    -- i in parentheses sometimes displays wrong on the OTN site
            dbms_output.put      ( TO_CHAR ( e#_list (j)
                                           , '999999999999'
            dbms_output.put      ('   ');
            dbms_output.put_line (name_list (j)); 
        END LOOP; 
    END IF; 
END verify; 
SHOW ERRORS
Here's the output I get when I run the procedure above with your sample data:
The following employees are both drivers and mechanics:
            1   John Smith
You'll notice I made several other changes in your code, sometimes because they are clearly better practices, and sometimes just to show you different ways to do the same thing, which you may or may not want to use in this problem.
For example, you were doing the same query (with only very slight differences) 2 times: once to get no_of_duplicates, and then a second time to get the actual data.  I don't know if that's the most efficient way to do what you need.  Say there are 1000 rows in the result set.  You'll fetch all 1000 once just to get the total number, (which you don't need, if all you care about at this point is if there are any), and then to get the data.  When you do a BULK COLLECT, you automatically get the COUNT anyway, so why not do the BULK COLLECT first, then use that COUNT to see what you have to do next.  If the COUNT is more than 0, then you've already got the data, and you don't need to fetch it again.  Also, repeating (essentially) the same code is a maintenance problem.  If you ever need to make a change, you need to make the same change in multiple places.  At best, that's a pain; but this is the exactly the kind of mistake that is easy to miss in in testing, and you might have code running for weeks in Production before you notice that sometimes it's giving the wrong results.
Another example: e# is a NUMBER.  While it is possible to convert NUMBERs into VARCHAR2s, and then store those VARCHAR2s in a VARCHAR2 collecction, wouldn't it make more sense just to store them in a NUMBER collection?