There is nothing to update so what is wrong?

Question

I have tried different ways but there is nothing to update so
what is wrong?
1 CREATE OR REPLACE PROCEDURE Update_Enrollment
2 (p_stuid IN NUMBER,
3 P_sectionid IN NUMBER,
4 p_grade IN CHAR)
5 AS
6 BEGIN
7 UPDATE Update_Enrollment
8 SET stuid = p_stuid
9 WHERE sectionid = p_sectionid
10 AND grade = p_grade;
11 COMMIT;
12 DBMS_OUTPUT.PUT_LINE ('Enrollment updated');
13 EXCEPTION
14 WHEN OTHERS THEN
15 DBMS_OUTPUT.PUT_LINE ('An error occurred');
16* END Update_Enrollment;
SQL> /
Warning: Procedure created with compilation errors.
SQL> ed
Wrote file afiedt.buf
1 CREATE OR REPLACE PROCEDURE Update_Enrollment
2 (p_stuid IN NUMBER,
3 P_sectionid IN NUMBER,
4 p_grade IN CHAR)
5 AS
6 BEGIN
7 UPDATE enrollment
8 SET stuid = p_stuid
9 WHERE sectionid = p_sectionid
10 AND grade = p_grade;
11 COMMIT;
12 DBMS_OUTPUT.PUT_LINE ('Enrollment updated');
13 EXCEPTION
14 WHEN OTHERS THEN
15 DBMS_OUTPUT.PUT_LINE ('An error occurred');
16* END Update_Enrollment;
SQL> /
Procedure created.
SQL> EXEC Update_Enrollment ('1','11','B')
PL/SQL procedure successfully completed.
SQL> SELECT stuid, sectionid, grade
2 FROM enrollment
3 /
STUID SECTIONID G
3 1
3 8
3 11
4 1
4 8
4 11
6 1
6 8
6 11
1 4
1 14
STUID SECTIONID G
2 4
2 14
5 4
5 14
15 rows selected.
SQL> EXEC Update_Enrollment (1, 11, 'B')
PL/SQL procedure successfully completed.
SQL> SELECT stuid, sectionid, grade
2 FROM enrollment
3 /
STUID SECTIONID G
3 1
3 8
3 11
4 1
4 8
4 11
6 1
6 8
6 11
1 4
1 14
STUID SECTIONID G
2 4
2 14
5 4
5 14
15 rows selected.

Answer 1

Beau,
Please read my latest response to your other post first before
reading this one:
http://forums.oracle.com/forums/message.jsp?id=644453
You can use SQL%ROWCOUNT to tell you how many records (rows) in
the table were updated by your procedure:
Modifying the procedure from your other post to use SQL%ROWCOUNT:
SQL> CREATE OR REPLACE PROCEDURE update_enrollment
  2    (p_stuid     IN NUMBER,
  3       p_sectionid IN NUMBER,
  4       p_grade     IN VARCHAR2)
  5  AS
  6  BEGIN
  7    UPDATE enrollment
  8    SET    grade = p_grade
  9    WHERE  stuid = p_stuid
10    AND    sectionid = p_sectionid;
11 
12    DBMS_OUTPUT.PUT_LINE (SQL%ROWCOUNT || ' records
updated.');
13 
14    COMMIT;
15 
16  EXCEPTION
17    WHEN OTHERS THEN
18        DBMS_OUTPUT.PUT_LINE ('An error occurred');
19  END update_enrollment;
20  /
Procedure created.
And, if this is your data:
SQL> SELECT stuid, sectionid, grade
  2  FROM   enrollment
  3  /
     STUID  SECTIONID G                
         3          1                  
         3          8                  
         3         11                  
         4          1                  
         4          8                  
         4         11                  
         6          1                  
         6          8                  
         6         11                  
         1          4                  
         1         14                  
         2          4                  
         2         14                  
         5          4                  
         5         14                  
15 rows selected.
There is no existing record (row) where stuid = 1 and sectionid
= 11:
SQL> SELECT stuid, sectionid, grade
  2  FROM   enrollment
  3  WHERE  stuid = 1
  4  AND    sectionid = 11
  5  /
no rows selected
So, if you execute your procedure and tell it to set (change)
the grade to 'B' in all existing records (rows) where the stuid
is 1 and the sectionid is 11:
Remembering to SET SERVEROUTPUT ON so that the messages
displayed by DBMS_OUTPUT.PUT_LINE can be seen:
SQL> SET SERVEROUTPUT ON
SQL> EXEC update_enrollment (1, 11, 'B')
0 records updated.                     
PL/SQL procedure successfully completed.
The procedure executes successfully because it updated all such
rows.  It just so happens that there aren't any such rows, so it
successfully updated zero rows and tells you that.
There does happen to be an existing record (row) in the table
where the stuid is 1 and the sectionid is 4:
SQL> SELECT stuid, sectionid, grade
  2  FROM   enrollment
  3  WHERE  stuid = 1
  4  AND    sectionid = 4
  5  /
     STUID  SECTIONID G                
         1          4                  
So, if you tell your procedure to set (change) the grade to 'B'
in all existing records (rows) where stuid = 1 and sectionid = 4:
Remembering to SET SERVEROUTPUT ON so that the messages
displayed by DBMS_OUTPUT.PUT_LINE can be seen:
SQL> SET SERVEROUTPUT ON
SQL> EXEC update_enrollment (1, 4, 'B')
1 records updated.                     
PL/SQL procedure successfully completed.
Then, the procedure executes successfully updating all such
existing records (rows).  In this case there is one such row and
the grade in that row has now been set (chaged) to 'B' and it
tells you that 1 row was updated.
SQL> SELECT stuid, sectionid, grade
  2  FROM   enrollment
  3  /
     STUID  SECTIONID G                
         3          1                  
         3          8                  
         3         11                  
         4          1                  
         4          8                  
         4         11                  
         6          1                  
         6          8                  
         6         11                  
         1          4 B                
         1         14                  
         2          4                  
         2         14                  
         5          4                  
         5         14                  
15 rows selected.
The above is only one very simple usage.  You could add
additional code to display a certain message if the SQL%ROWCOUNT
is 0.  As John said, you could raise a user-defined exception. 
Modifying your procedure to do that:
SQL> CREATE OR REPLACE PROCEDURE update_enrollment
  2    (p_stuid     IN NUMBER,
  3       p_sectionid IN NUMBER,
  4       p_grade     IN VARCHAR2)
  5  AS
  6    e_zero_rows     EXCEPTION;
  7  BEGIN
  8    UPDATE enrollment
  9    SET    grade = p_grade
10    WHERE  stuid = p_stuid
11    AND    sectionid = p_sectionid;
12 
13    DBMS_OUTPUT.PUT_LINE (SQL%ROWCOUNT || ' records
updated.');
14 
15    IF SQL%ROWCOUNT = 0
16    THEN
17        RAISE e_zero_rows;
18    ELSE
19        COMMIT;
20    END IF;
21  EXCEPTION
22    WHEN e_zero_rows THEN
23        DBMS_OUTPUT.PUT_LINE ('No rows were updated.');
24        DBMS_OUTPUT.PUT_LINE ('SQL%ROWCOUNT was 0');
25    WHEN OTHERS THEN
26        DBMS_OUTPUT.PUT_LINE ('An error occurred');
27  END update_enrollment;
28  /
Procedure created.
Then, if you execute your procedure and tell it to set (change)
the grade to 'B' in all existing records (rows) where the stuid
is 1 and the sectionid is 11:
Remembering to SET SERVEROUTPUT ON so that the messages
displayed by DBMS_OUTPUT.PUT_LINE can be seen:
SQL> SET SERVEROUTPUT ON
SQL> EXEC update_enrollment (1, 11, 'B')
0 records updated.                     
No rows were updated.                  
SQL%ROWCOUNT was 0                     
PL/SQL procedure successfully completed.
Then you get a more meaningful error message.  This gives you a
better idea of what went wrong.  The user-defined exception is
one method.
There are other methods for handling exceptions.  Suppose, for
example, that you don't have anything to handle exceptions in
your procedure and you attempt to enter an invalid grade:
SQL> CREATE OR REPLACE PROCEDURE update_enrollment
  2    (p_stuid     IN NUMBER,
  3       p_sectionid IN NUMBER,
  4       p_grade     IN VARCHAR2)
  5  AS
  6    e_zero_rows     EXCEPTION;
  7  BEGIN
  8    UPDATE enrollment
  9    SET    grade = p_grade
10    WHERE  stuid = p_stuid
11    AND    sectionid = p_sectionid;
12 
13    DBMS_OUTPUT.PUT_LINE (SQL%ROWCOUNT || ' records
updated.');
14 
15    COMMIT;
16  END update_enrollment;
17  /
Procedure created.
SQL> SET SERVEROUTPUT ON
SQL> EXEC update_enrollment (1, 4, 'Z')
BEGIN update_enrollment (1, 4, 'Z'); END;
ERROR at line 1:
ORA-02290: check constraint
(SCOTT.CHECK_GRADE) violated
ORA-06512: at
"SCOTT.UPDATE_ENROLLMENT", line 8
ORA-06512: at line 1
The above message tells you that you violated a check constraint
and your procedure was not completed.  However, if you did the
same thing, with this sort of exception handling:
SQL> CREATE OR REPLACE PROCEDURE update_enrollment
  2    (p_stuid     IN NUMBER,
  3       p_sectionid IN NUMBER,
  4       p_grade     IN VARCHAR2)
  5  AS
  6    e_zero_rows     EXCEPTION;
  7  BEGIN
  8    UPDATE enrollment
  9    SET    grade = p_grade
10    WHERE  stuid = p_stuid
11    AND    sectionid = p_sectionid;
12 
13    DBMS_OUTPUT.PUT_LINE (SQL%ROWCOUNT || ' records
updated.');
14 
15    COMMIT;
16  EXCEPTION
17    WHEN OTHERS THEN
18        DBMS_OUTPUT.PUT_LINE ('An error occurred.');
19  END update_enrollment;
20  /
Procedure created.
SQL> SET SERVEROUTPUT ON
SQL> EXEC update_enrollment (1, 4, 'Z')
An error occurred.                     
PL/SQL procedure successfully completed.
Then, the only message you get is that an error occurred, with
no clue as to what type of error.  This is what David was
talking about in the other post.  You would probably be better
off without any exception handling than leaving it this way. 
You could however do something like this:
SQL> CREATE OR REPLACE PROCEDURE update_enrollment
  2    (p_stuid     IN NUMBER,
  3       p_sectionid IN NUMBER,
  4       p_grade     IN VARCHAR2)
  5  AS
  6    e_zero_rows     EXCEPTION;
  7  BEGIN
  8    UPDATE enrollment
  9    SET    grade = p_grade
10    WHERE  stuid = p_stuid
11    AND    sectionid = p_sectionid;
12 
13    DBMS_OUTPUT.PUT_LINE (SQL%ROWCOUNT || ' records
updated.');
14 
15    COMMIT;
16  EXCEPTION
17    WHEN OTHERS THEN
18        DBMS_OUTPUT.PUT_LINE (sqlerrm (sqlcode));
19  END update_enrollment;
20  /
Procedure created.
SQL> SET SERVEROUTPUT ON
SQL> EXEC update_enrollment (1, 4, 'Z')
ORA-02290: check constraint            
(SCOTT.CHECK_GRADE) violated           
PL/SQL procedure successfully completed.
The above traps and displays the error message, but allows your
procedure to complete.
The exception handling may be a little beyond what is expected
in your class at this time.  You might ask your instructor about
it.  There are also other methods of handling exceptions.
Barbara
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