, , ,

NonPredefined Error

To handle unnamed internal exceptions, you must use the OTHERS handler or the pragma EXCEPTION_INIT. A pragma is a compiler directive, which can be thought of as a parenthetical remark to the compiler. Pragmas (also called pseudoinstructions)
are processed at compile time, not at run time.
In PL/SQL, the pragma EXCEPTION_INIT tells the compiler to associate an exception name with an Oracle error number. That allows you to refer to any internal exception by name and to write a specific handler for it. You code the pragma EXCEPTION_INIT in the declarative part of a PL/SQL block, subprogram, or package using the syntax
PRAGMA EXCEPTION_INIT(exception_name, Oracle_error_number);
where exception_name is the name of a previously declared exception. The pragma must appear somewhere after the exception declaration in the same declarative section, as shown in the following example:

/by
, , ,

Predefined Exceptions

An internal exception is raised implicitly whenever your PL/SQL program violates an Oracle rule or exceeds a system-dependent limit. Every Oracle error has a number, but exceptions must be handled by name. So, PL/SQL predefines some common Oracle errors as exceptions. For example, PL/SQL raises the predefined exception NO_DATA_FOUND if a SELECT INTO statement returns no rows.
To handle other Oracle errors, you can use the OTHERS handler. The functions SQLCODE and SQLERRM are especially useful in the OTHERS handler because they return the Oracle error code and message text. Alternatively, you can use the pragma EXCEPTION_INIT to associate exception names with Oracle error codes.
PL/SQL declares predefined exceptions globally in package STANDARD, which defines the PL/SQL environment. So, you need not declare them yourself. You can write handlers for predefined exceptions using the names shown in the list below. Also shown are the corresponding Oracle error codes and SQLCODE return values.

/by
, , ,

User-Defined Exceptions

PL/SQL lets you define exceptions of your own. Unlike predefined exceptions, user-defined exceptions must be declared and must be raised explicitly by RAISE statements.

/by
, , ,

Exception Handling in PL SQL

In PL/SQL, a warning or error condition is called an exception. Exceptions can be internally defined (by the run-time system) or user defined. Examples of internally defined exceptions include division by zero and out of memory. Some common internal exceptions have predefined names, such as ZERO_DIVIDE and STORAGE_ERROR. The other internal exceptions can be given names.

 
Exception Types
There are three types of exception
 
Exception Handlers 
 
Trapping an Exception:
If the exception is raised in the executable section of the block, processing branches to the corresponding exception handler in the exception section of the block. If PL/SQL successfully handles the exception, then the exception does not propagate to the enclosing block or environment. The PL/SQL block terminates successfully.

Propagating an Exception:
If the exception is raised in the executable section of the block and there is no corresponding exception handler, the PL/SQL block terminates with failure and the exception is propagated to the calling environment.

/by
, , ,

PL SQL Cursors

A cursor is the Private Memory area which is created by an Oracle server for manipulating the data.
Two Types of CURSORS
    1.  EXPLICIT : Multiple row SELECT  STATEMENTS
    2.  IMPLICIT
        All INSERT statements
        All UPDATE statements
        All DELETE statements
        Single row SELECT….INTO Statements
Using Explicit Cursors
The set of rows returned by a query can consist of zero, one, or multiple rows, depending on how many rows meet your search criteria. When a query returns multiple rows, you can explicitly declare a cursor to process the rows. Moreover,
you can declare a cursor in the declarative part of any PL/SQL block, subprogram, or package.
You use three commands to control a cursor: OPEN, FETCH, and CLOSE. First, you initialize the cursor with the OPEN statement, which identifies the result set. Then, you use the FETCH statement to retrieve the first row. You can execute FETCH repeatedly until all rows have been retrieved. When the last row has been processed, you release the cursor with the CLOSE statement. You can process several queries in parallel by declaring and opening multiple cursors.

Using Cursor FOR Loops
In most situations that require an explicit cursor, you can simplify coding by using a cursor FOR loop instead of the OPEN, FETCH, and CLOSE statements. A cursor FOR loop implicitly declares its loop index as a %ROWTYPE record, opens a cursor,
repeatedly fetches rows of values from the result set into fields in the record, and closes the cursor when all rows have been processed.
Consider the PL/SQL block below, which computes results from an experiment, then stores the results in a temporary table. The FOR loop index c1_rec is implicitly declared as a record. Its fields store all the column values fetched from the cursor c1. Dot notation is used to reference individual fields.
DECLARE
result temp.col1%TYPE;
CURSOR c1 IS
SELECT n1, n2, n3 FROM data_table WHERE exper_num = 1;
BEGIN
FOR c1_rec IN c1 LOOP
/* calculate and store the results */
result := c1_rec.n2 / (c1_rec.n1 + c1_rec.n3);
INSERT INTO temp VALUES (result, NULL, NULL);
END LOOP;
COMMIT;
END; Passing Parameters
You can pass parameters to the cursor in a cursor FOR loop. In the following example, you pass a department number. Then, you compute the total wages paid to employees in that department. Also, you determine how many employees have
salaries higher than $2000 and/or commissions larger than their salaries.
— available online in file ’examp8’
DECLARE
CURSOR emp_cursor(dnum NUMBER) IS
SELECT sal, comm FROM emp WHERE deptno = dnum;
total_wages NUMBER(11,2) := 0;
high_paid NUMBER(4) := 0;
higher_comm NUMBER(4) := 0;
BEGIN
/* The number of iterations will equal the number of rows
returned by emp_cursor. */
FOR emp_record IN emp_cursor(20) LOOP
emp_record.comm := NVL(emp_record.comm, 0);
total_wages := total_wages + emp_record.sal +
emp_record.comm;
IF emp_record.sal > 2000.00 THEN
high_paid := high_paid + 1;
END IF;
IF emp_record.comm > emp_record.sal THEN
higher_comm := higher_comm + 1;
END IF;
END LOOP;
INSERT INTO temp VALUES (high_paid, higher_comm,
’Total Wages: ’ || TO_CHAR(total_wages));
COMMIT;
END;
Implicit Cursors – FOR Loops
An Implicit Cursor is automatically associated with any SQL DML statement that does not have an explicit cursor associated with it.
This includes :
     1. ALL INSERT      statements 
     2. ALL UPDATE      statements
     3. ALL DELETE      statements
     4. ALL SELECT…INTO statements
QuickNotes – Implicit Cursors
1. Implicit cursor is called the “SQL” cursor –it stores information concerning the processing of the last  SQL  statement not associated with an explicit cursor.
2.OPEN, FETCH, AND CLOSE don’t apply.
3. All cursor attributes apply.

FOR UPDATE Clause
  • Use explicit locking to deny access for the duration of a transaction
  • Locks the rows before update or delete .

Syntax:  Select …..
     from
     FOR UPDATE  [ OF column reference ] [NOWAIT];e.g.
Declare
    Cursor EmpCursor is
    select emp_id, last_name, dept_name
    from employees , department
    where employees.dept_id=department.dept_id
    and employees.dept_id=80
    FOR UPDATE OF salary NOWAIT;

/by