1 Overview of PL/SQL

Declaring Variables

Variables can have any SQL datatype, such as CHAR, DATE, or NUMBER, or a PL/SQL-only datatype, such as BOOLEAN or PLS_INTEGER. For example, assume that you want to declare variables for part data, such as part_no to hold 6-digit numbers and in_stock to hold the Boolean value TRUE or FALSE. You declare these and related part variables as shown in Example 1-1. Note that there is a semi-colon (;) at the end of each line in the declaration section.

DECLARE
  part_no    NUMBER(6);
  part_name  VARCHAR2(20);
  in_stock   BOOLEAN;
  part_price NUMBER(6,2);
  part_desc  VARCHAR2(50);

You can also declare nested tables, variable-size arrays (varrays for short), and records using the TABLE, VARRAY, and RECORD composite datatypes. See Chapter 5, "Using PL/SQL Collections and Records".

Assigning Values to a Variable

You can assign values to a variable in three ways. The first way uses the assignment operator (:=), a colon followed by an equal sign, as shown in Example 1-2. You place the variable to the left of the operator and an expression, including function calls, to the right. Note that you can assign a value to a variable when it is declared.

DECLARE
   wages          NUMBER;
   hours_worked   NUMBER := 40;
   hourly_salary  NUMBER := 22.50;
   bonus          NUMBER := 150;
   country        VARCHAR2(128);
   counter        NUMBER := 0;
   done           BOOLEAN;
   valid_id       BOOLEAN;
   emp_rec1       employees%ROWTYPE;
   emp_rec2       employees%ROWTYPE;
   TYPE commissions IS TABLE OF NUMBER INDEX BY PLS_INTEGER;
   comm_tab       commissions;
BEGIN
   wages := (hours_worked * hourly_salary) + bonus;
   country := 'France';
   country := UPPER('Canada');
   done := (counter > 100);
   valid_id := TRUE;
   emp_rec1.first_name := 'Antonio';
   emp_rec1.last_name := 'Ortiz';
   emp_rec1 := emp_rec2;
   comm_tab(5) := 20000 * 0.15;
END;
/

The second way to assign values to a variable is by selecting (or fetching) database values into it. In Example 1-3, 10% of an employee's salary is selected into the bonus variable. Now you can use the bonus variable in another computation or insert its value into a database table.

DECLARE
  bonus  NUMBER(8,2);
  emp_id NUMBER(6) := 100;
BEGIN
  SELECT salary * 0.10 INTO bonus FROM employees 
    WHERE employee_id = emp_id;
END;
/

The third way to assign a value to a variable is by passing it as an OUT or IN OUT parameter to a subprogram, and then assigning the value inside the subprogram. Example 1-4 passes the sal variable to a subprogram, and the subprogram updates the variable.

In the example, DBMS_OUTPUT.PUT_LINE is used to display output from the PL/SQL program. For more information, see "Inputting and Outputting Data with PL/SQL". For information on the DBMS_OUTPUT package, see "About the DBMS_OUTPUT Package".

REM SERVEROUTPUT must be set to ON to display output with DBMS_OUTPUT
SET SERVEROUTPUT ON FORMAT WRAPPED
DECLARE
  new_sal NUMBER(8,2);
  emp_id  NUMBER(6) := 126;
  PROCEDURE adjust_salary(emp_id NUMBER, sal IN OUT NUMBER) IS  
    emp_job VARCHAR2(10);
    avg_sal NUMBER(8,2);
    BEGIN
      SELECT job_id INTO emp_job FROM employees WHERE employee_id = emp_id;
      SELECT AVG(salary) INTO avg_sal FROM employees WHERE job_id = emp_job;
      DBMS_OUTPUT.PUT_LINE ('The average salary for ' || emp_job 
                            || ' employees: ' || TO_CHAR(avg_sal));
      sal := (sal + avg_sal)/2; -- adjust sal value which is returned
    END; 
BEGIN
  SELECT AVG(salary) INTO new_sal FROM employees;
  DBMS_OUTPUT.PUT_LINE ('The average salary for all employees: ' 
                        || TO_CHAR(new_sal));
  adjust_salary(emp_id, new_sal); -- assigns a new value to new_sal
  DBMS_OUTPUT.PUT_LINE ('The adjusted salary for employee ' || TO_CHAR(emp_id) 
                        || ' is ' || TO_CHAR(new_sal)); -- sal has new value
END;
/

Bind Variables

When you embed an INSERT, UPDATE, DELETE, or SELECT SQL statement directly in your PL/SQL code, PL/SQL turns the variables in the WHERE and VALUES clauses into bind variables automatically. Oracle can reuse these SQL statement each time the same code is executed. To run similar statements with different variable values, you can save parsing overhead by calling a stored procedure that accepts parameters, then issues the statements with the parameters substituted in the appropriate places.

You do need to specify bind variables with dynamic SQL, in clauses like WHERE and VALUES where you normally use variables. Instead of concatenating literals and variable values into a single string, replace the variables with the names of bind variables (prefixed by a colon) and specify the corresponding PL/SQL variables with the USING clause. Using the USING clause, instead of concatenating the variables into the string, reduces parsing overhead and lets Oracle reuse the SQL statements. For example:

'DELETE FROM employees WHERE employee_id = :id' USING emp_id;

For an example of the use of bind variables, see Example 7-1.

Declaring Constants

Declaring a constant is like declaring a variable except that you must add the keyword CONSTANT and immediately assign a value to the constant. No further assignments to the constant are allowed. The following example declares a constant:

credit_limit CONSTANT NUMBER := 5000.00;

See "Constants".

%TYPE

The %TYPE attribute provides the datatype of a variable or database column. This is particularly useful when declaring variables that will hold database values. For example, assume there is a column named last_name in a table named employees. To declare a variable named v_last_name that has the same datatype as column title, use dot notation and the %TYPE attribute, as follows:

Declaring v_last_name with %TYPE has two advantages. First, you need not know the exact datatype of last_name. Second, if you change the database definition of last_name, perhaps to make it a longer character string, the datatype of v_last_name changes accordingly at run time.

For more information on %TYPE, see "Using the %TYPE Attribute" and "%TYPE Attribute".

%ROWTYPE

In PL/SQL, records are used to group data. A record consists of a number of related fields in which data values can be stored. The %ROWTYPE attribute provides a record type that represents a row in a table. The record can store an entire row of data selected from the table or fetched from a cursor or cursor variable. See "Cursors".

Columns in a row and corresponding fields in a record have the same names and datatypes. In the following example, you declare a record named dept_rec. Its fields have the same names and datatypes as the columns in the departments table.

You use dot notation to reference fields, as the following example shows:

If you declare a cursor that retrieves the last name, salary, hire date, and job class of an employee, you can use %ROWTYPE to declare a record that stores the same information as shown in Example 1-6. When you execute the FETCH statement, the value in the last_name column of the employees table is assigned to the last_name field of employee_rec, the value in the salary column is assigned to the salary field, and so on.

DECLARE
  CURSOR c1 IS
    SELECT last_name, salary, hire_date, job_id FROM employees 
       WHERE employee_id = 120;
-- declare record variable that represents a row fetched from the employees table
   employee_rec c1%ROWTYPE; 
BEGIN
-- open the explicit cursor and use it to fetch data into employee_rec
  OPEN c1;
  FETCH c1 INTO employee_rec;
  DBMS_OUTPUT.PUT_LINE('Employee name: ' || employee_rec.last_name);
END;
/

For more information on %ROWTYPE, see "Using the %ROWTYPE Attribute" and "%ROWTYPE Attribute".

Conditional Control

Often, it is necessary to take alternative actions depending on circumstances. The IF-THEN-ELSE statement lets you execute a sequence of statements conditionally. The IF clause checks a condition, the THEN clause defines what to do if the condition is true and the ELSE clause defines what to do if the condition is false or null. Example 1-7 shows the use of IF-THEN-ELSE to determine the salary raise an employee receives based on the current salary of the employee.

To choose among several values or courses of action, you can use CASE constructs. The CASE expression evaluates a condition and returns a value for each case. The case statement evaluates a condition and performs an action, such as an entire PL/SQL block, for each case. See Example 1-7.

DECLARE
   jobid      employees.job_id%TYPE;
   empid      employees.employee_id%TYPE := 115;
   sal        employees.salary%TYPE;
   sal_raise  NUMBER(3,2);
BEGIN
  SELECT job_id, salary INTO jobid, sal from employees WHERE employee_id = empid;
  CASE
    WHEN jobid = 'PU_CLERK' THEN
        IF sal < 3000 THEN sal_raise := .12;
          ELSE sal_raise := .09;
        END IF;
    WHEN jobid = 'SH_CLERK' THEN
        IF sal < 4000 THEN sal_raise := .11;
          ELSE sal_raise := .08;
        END IF;
    WHEN jobid = 'ST_CLERK' THEN
        IF sal < 3500 THEN sal_raise := .10;
          ELSE sal_raise := .07;
        END IF;
    ELSE
     BEGIN
       DBMS_OUTPUT.PUT_LINE('No raise for this job: ' || jobid);
     END;
  END CASE;
  UPDATE employees SET salary = salary + salary * sal_raise 
    WHERE employee_id = empid;
  COMMIT;
END;
/

A sequence of statements that uses query results to select alternative actions is common in database applications. Another common sequence inserts or deletes a row only if an associated entry is found in another table. You can bundle these common sequences into a PL/SQL block using conditional logic.

Iterative Control

LOOP statements let you execute a sequence of statements multiple times. You place the keyword LOOP before the first statement in the sequence and the keywords END LOOP after the last statement in the sequence. The following example shows the simplest kind of loop, which repeats a sequence of statements continually:

The FOR-LOOP statement lets you specify a range of integers, then execute a sequence of statements once for each integer in the range. In Example 1-8 the loop inserts 100 numbers, square roots, squares, and the sum of squares into a database table:

CREATE TABLE sqr_root_sum (num NUMBER, sq_root NUMBER(6,2),
                           sqr NUMBER, sum_sqrs NUMBER);
DECLARE
   s PLS_INTEGER;
BEGIN
  FOR i in 1..100 LOOP
    s := (i * (i + 1) * (2*i +1)) / 6; -- sum of squares
    INSERT INTO sqr_root_sum VALUES (i, SQRT(i), i*i, s );
  END LOOP;
END;
/

The WHILE-LOOP statement associates a condition with a sequence of statements. Before each iteration of the loop, the condition is evaluated. If the condition is true, the sequence of statements is executed, then control resumes at the top of the loop. If the condition is false or null, the loop is bypassed and control passes to the next statement.

In Example 1-9, you find the first employee who has a salary over $15000 and is higher in the chain of command than employee 120:

CREATE TABLE temp (tempid NUMBER(6), tempsal NUMBER(8,2), tempname VARCHAR2(25));
DECLARE
   sal            employees.salary%TYPE := 0;
   mgr_id         employees.manager_id%TYPE;
   lname          employees.last_name%TYPE;
   starting_empid employees.employee_id%TYPE := 120;
BEGIN
   SELECT manager_id INTO mgr_id FROM employees 
      WHERE employee_id = starting_empid;
   WHILE sal <= 15000 LOOP -- loop until sal > 15000
      SELECT salary, manager_id, last_name INTO sal, mgr_id, lname
         FROM employees WHERE employee_id = mgr_id;
   END LOOP;
   INSERT INTO temp VALUES (NULL, sal, lname); -- insert NULL for tempid
   COMMIT;
EXCEPTION
   WHEN NO_DATA_FOUND THEN
      INSERT INTO temp VALUES (NULL, NULL, 'Not found'); -- insert NULLs
      COMMIT;
END;
/

The EXIT-WHEN statement lets you complete a loop if further processing is impossible or undesirable. When the EXIT statement is encountered, the condition in the WHEN clause is evaluated. If the condition is true, the loop completes and control passes to the next statement. In Example 1-10, the loop completes when the value of total exceeds 25,000:

DECLARE
  total   NUMBER(9) := 0;
  counter NUMBER(6) := 0;
BEGIN
  LOOP
    counter := counter + 1;
    total := total + counter * counter;
    -- exit loop when condition is true
    EXIT WHEN total > 25000;  
  END LOOP;
  DBMS_OUTPUT.PUT_LINE('Counter: ' || TO_CHAR(counter) || ' Total: ' || TO_CHAR(total));
END;
/

Sequential Control

The GOTO statement lets you branch to a label unconditionally. The label, an undeclared identifier enclosed by double angle brackets, must precede an executable statement or a PL/SQL block. When executed, the GOTO statement transfers control to the labeled statement or block, as shown in Example 1-11.

DECLARE
  total   NUMBER(9) := 0;
  counter NUMBER(6) := 0;
BEGIN
  <<calc_total>>
    counter := counter + 1;
    total := total + counter * counter;
    -- branch to print_total label when condition is true
    IF total > 25000 THEN GOTO print_total;
      ELSE GOTO calc_total;
    END IF;
  <<print_total>>
  DBMS_OUTPUT.PUT_LINE('Counter: ' || TO_CHAR(counter) || ' Total: ' || TO_CHAR(total));
END;
/

Subprograms: Procedures and Functions

There are two types of subprograms called procedures and functions, which can accept parameters and be invoked (called). See "What Are Subprograms?".

The SQL CREATE PROCEDURE statement lets you create standalone procedures that are stored in the database. For information, see CREATE PROCEDURE in Oracle Database SQL Reference. The SQL CREATE FUNCTION statement lets you create standalone functions that are stored in an Oracle database. For information, see CREATE FUNCTION in Oracle Database SQL Reference. These stored (schema level) subprograms can be accessed from SQL.

As shown in Example 1-12, a subprogram is like a miniature program, beginning with a header followed by an optional declarative part, an executable part, and an optional exception-handling part.

-- including OR REPLACE is more convenient when updating a subprogram
CREATE OR REPLACE PROCEDURE award_bonus (emp_id NUMBER, bonus NUMBER) AS
   commission        REAL;
   comm_missing EXCEPTION;
BEGIN  -- executable part starts here
   SELECT commission_pct / 100 INTO commission FROM employees
    WHERE employee_id = emp_id;
   IF commission IS NULL THEN
      RAISE comm_missing;
   ELSE
      UPDATE employees SET salary = salary + bonus*commission 
      WHERE employee_id = emp_id;
   END IF;
EXCEPTION  -- exception-handling part starts here
   WHEN comm_missing THEN
      DBMS_OUTPUT.PUT_LINE('This employee does not receive a commission.');
      commission := 0;
   WHEN OTHERS THEN
      NULL; -- for other exceptions do nothing
END award_bonus;
/
CALL award_bonus(150, 400);

When called, this procedure accepts an employee Id and a bonus amount. It uses the Id to select the employee's commission percentage from a database table and, at the same time, convert the commission percentage to a decimal amount. Then, it checks the commission amount. If the commission is null, an exception is raised; otherwise, the employee's salary is updated.

Packages: APIs Written in PL/SQL

PL/SQL lets you bundle logically related types, variables, cursors, and subprograms into a package, a database object that is a step above regular stored procedures. The packages defines a simple, clear, interface to a set of related procedures and types that can be accessed by SQL statements.

Packages usually have two parts: a specification and a body. The specification defines the application programming interface; it declares the types, constants, variables, exceptions, cursors, and subprograms. The body fills in the SQL queries for cursors and the code for subprograms.

To create package specs, use the SQL statement CREATE PACKAGE. A CREATE PACKAGE BODY statement defines the package body. For information on the CREATE PACKAGE SQL statement, see Oracle Database SQL Reference. For information on the CREATE PACKAGE BODY SQL statement, see Oracle Database SQL Reference.

In Example 1-13, the emp_actions package contain two procedures that update the employees table and one function that provides information.

CREATE OR REPLACE PACKAGE emp_actions AS  -- package specification
   PROCEDURE hire_employee (employee_id NUMBER, last_name VARCHAR2, 
     first_name VARCHAR2, email VARCHAR2, phone_number VARCHAR2,
    hire_date DATE, job_id VARCHAR2, salary NUMBER, commission_pct NUMBER,
    manager_id NUMBER, department_id NUMBER);
   PROCEDURE fire_employee (emp_id NUMBER);
   FUNCTION num_above_salary (emp_id NUMBER) RETURN NUMBER;
END emp_actions;
/
CREATE OR REPLACE PACKAGE BODY emp_actions AS  -- package body
-- code for procedure hire_employee
   PROCEDURE hire_employee (employee_id NUMBER, last_name VARCHAR2,
      first_name VARCHAR2, email VARCHAR2, phone_number VARCHAR2, hire_date DATE,
      job_id VARCHAR2, salary NUMBER, commission_pct NUMBER,
      manager_id NUMBER, department_id NUMBER) IS
   BEGIN
      INSERT INTO employees VALUES (employee_id, last_name, first_name, email,
       phone_number, hire_date, job_id, salary, commission_pct, manager_id,
       department_id);
   END hire_employee;
-- code for procedure fire_employee
   PROCEDURE fire_employee (emp_id NUMBER) IS
   BEGIN
      DELETE FROM employees WHERE employee_id = emp_id;
   END fire_employee;
-- code for function num_above salary
   FUNCTION num_above_salary (emp_id NUMBER) RETURN NUMBER IS
      emp_sal NUMBER(8,2);
      num_count NUMBER;
   BEGIN
      SELECT salary INTO emp_sal FROM employees WHERE employee_id = emp_id;
      SELECT COUNT(*) INTO num_count FROM employees WHERE salary > emp_sal;
      RETURN num_count;
   END num_above_salary;
END emp_actions;
/

Applications that call these procedures only need to know the names and parameters from the package specification. You can change the implementation details inside the package body without affecting the calling applications.

To call the procedures of the emp_actions package created in Example 1-13, you can execute the statements in Example 1-14. The procedures can be executed in a BEGIN .. END block or with the SQL CALL statement. Note the use of the package name as a prefix to the procedure name.

CALL emp_actions.hire_employee(300, 'Belden', 'Enrique', 'EBELDEN',
   '555.111.2222', '31-AUG-04', 'AC_MGR', 9000, .1, 101, 110);

BEGIN
  DBMS_OUTPUT.PUT_LINE( 'Number of employees with higher salary: ' || 
                         TO_CHAR(emp_actions.num_above_salary(120)));
  emp_actions.fire_employee(300);
END;
/

Packages are stored in the database, where they can be shared by many applications. Calling a packaged subprogram for the first time loads the whole package and caches it in memory, saving on disk I/O for subsequent calls. Thus, packages enhance reuse and improve performance in a multiuser, multi-application environment. For information on packages, see Chapter 9, "Using PL/SQL Packages".

If a subprogram does not take any parameters, you can include an empty set of parentheses or omit the parentheses, both in PL/SQL and in functions called from SQL queries. For calls to a method that takes no parameters, an empty set of parentheses is optional within PL/SQL scopes but required within SQL scopes.

Cursors

A cursor is a name for a specific private SQL area in which information for processing the specific statement is kept. PL/SQL uses both implicit and explicit cursors. PL/SQL implicitly declares a cursor for all SQL data manipulation statements on a set of rows, including queries that return only one row. For queries that return more than one row, you can explicitly declare a cursor to process the rows individually. For example, Example 1-6 declares an explicit cursor.

For information on managing cursors with PL/SQL, see "Managing Cursors in PL/SQL".

Collections

PL/SQL collection types let you declare high-level datatypes similar to arrays, sets, and hash tables found in other languages. In PL/SQL, array types are known as varrays (short for variable-size arrays), set types are known as nested tables, and hash table types are known as associative arrays. Each kind of collection is an ordered group of elements, all of the same type. Each element has a unique subscript that determines its position in the collection. When declaring collections, you use a TYPE definition. See "Defining Collection Types and Declaring Collection Variables".

To reference an element, use subscript notation with parentheses, as shown in Example 1-15.

DECLARE
  TYPE staff_list IS TABLE OF employees.employee_id%TYPE;
  staff staff_list;
  lname employees.last_name%TYPE;
  fname employees.first_name%TYPE;
BEGIN
   staff := staff_list(100, 114, 115, 120, 122);
   FOR i IN staff.FIRST..staff.LAST LOOP
     SELECT last_name, first_name INTO lname, fname FROM employees 
       WHERE employees.employee_id = staff(i);
     DBMS_OUTPUT.PUT_LINE ( TO_CHAR(staff(i)) || ': ' || lname || ', ' || fname );
   END LOOP;
END;
/

Collections can be passed as parameters, so that subprograms can process arbitrary numbers of elements.You can use collections to move data into and out of database tables using high-performance language features known as bulk SQL.

For information on collections, see Chapter 5, "Using PL/SQL Collections and Records".

Records

Records are composite data structures whose fields can have different datatypes. You can use records to hold related items and pass them to subprograms with a single parameter. When declaring records, you use a TYPE definition. See "Defining and Declaring Records".

Example 1-16 shows how are records are declared.

DECLARE
   TYPE timerec IS RECORD (hours SMALLINT, minutes SMALLINT);
   TYPE meetin_typ IS RECORD (
      date_held DATE,
      duration  timerec,  -- nested record
      location  VARCHAR2(20),
      purpose   VARCHAR2(50));
BEGIN
-- NULL does nothing but allows unit to be compiled and tested
  NULL;
END;
/

You can use the %ROWTYPE attribute to declare a record that represents a row in a table or a row from a query result set, without specifying the names and types for the fields.

For information on records, see Chapter 5, "Using PL/SQL Collections and Records".

Object Types

PL/SQL supports object-oriented programming through object types. An object type encapsulates a data structure along with the functions and procedures needed to manipulate the data. The variables that form the data structure are known as attributes. The functions and procedures that manipulate the attributes are known as methods.

Object types reduce complexity by breaking down a large system into logical entities. This lets you create software components that are modular, maintainable, and reusable. Object-type definitions, and the code for the methods, are stored in the database. Instances of these object types can be stored in tables or used as variables inside PL/SQL code. Example 1-17 shows an object type definition for a bank account.

CREATE TYPE bank_account AS OBJECT ( 
  acct_number NUMBER(5),
  balance     NUMBER,
  status      VARCHAR2(10),
  MEMBER PROCEDURE open (SELF IN OUT NOCOPY bank_account, amount IN NUMBER),
  MEMBER PROCEDURE close (SELF IN OUT NOCOPY bank_account, num IN NUMBER,
                          amount OUT NUMBER),
  MEMBER PROCEDURE deposit (SELF IN OUT NOCOPY bank_account, num IN NUMBER,
                            amount IN NUMBER),
  MEMBER PROCEDURE withdraw (SELF IN OUT NOCOPY bank_account, num IN NUMBER,
                             amount IN NUMBER),
  MEMBER FUNCTION curr_bal  (num IN NUMBER) RETURN NUMBER );
/

For information on object types, see Oracle Database Application Developer's Guide - Object-Relational Features. For information on the use of PL/SQL with objects, see Chapter 12, "Using PL/SQL With Object Types".

Anonymous Blocks

Anonymous PL/SQL blocks can be submitted to interactive tools such as SQL*Plus and Enterprise Manager, or embedded in an Oracle Precompiler or OCI program. At run time, the program sends these blocks to the Oracle database, where they are compiled and executed.

Stored Subprograms

Subprograms can be compiled and stored in an Oracle database, ready to be executed. Once compiled, it is a schema object known as a stored procedure or stored function, which can be referenced by any number of applications connected to that database.

The SQL CREATE PROCEDURE statement lets you create standalone procedures that are stored in the database. For information, see CREATE PROCEDURE in Oracle Database SQL Reference. The SQL CREATE FUNCTION statement lets you create standalone functions that are stored in an Oracle database. For information, see CREATE FUNCTION in Oracle Database SQL Reference.

Subprograms are stored in a compact compiled form. When called, they are loaded and processed immediately. Subprograms take advantage of shared memory, so that only one copy of a subprogram is loaded into memory for execution by multiple users.

Stored subprograms defined within a package are known as packaged subprograms. Those defined independently are called standalone subprograms. Subprograms nested inside other subprograms or within a PL/SQL block are known as local subprograms, which cannot be referenced by other applications and exist only inside the enclosing block.

Stored subprograms are the key to modular, reusable PL/SQL code. Wherever you might use a JAR file in Java, a module in Perl, a shared library in C++, or a DLL in Visual Basic, you should use PL/SQL stored procedures, stored functions, and packages.

You can call stored subprograms from a database trigger, another stored subprogram, an Oracle Precompiler or OCI application, or interactively from SQL*Plus or Enterprise Manager. You can also configure a web server so that the HTML for a web page is generated by a stored subprogram, making it simple to provide a web interface for data entry and report generation.

Example 1-18 shows how you can call the stored subprogram in Example 1-12 from SQL*Plus using the CALL statement or using a BEGIN ... END block.

CALL award_bonus(179, 1000);

BEGIN
  award_bonus(179, 10000);
END;
/
-- using named notation
BEGIN award_bonus(emp_id=>179, bonus=>10000); END;
/

Using the BEGIN .. END block is recommended in several situations. Calling the subprogram from a BEGIN .. END block allows named or mixed notation for parameters which the CALL statement does not support. For information on named parameters, see "Using Positional, Named, or Mixed Notation for Subprogram Parameters". In addition, using the CALL statement can suppress an ORA-01403: no data found error that has not been handled in the PL/SQL subprogram.

For additional examples on calling PL/SQL procedures, see Example 8-5, "Subprogram Calls Using Positional, Named, and Mixed Notation" and "Passing Schema Object Names As Parameters". For information on the use of the CALL statement, see Oracle Database SQL Reference

Database Triggers

A database trigger is a stored subprogram associated with a database table, view, or event. The trigger can be called once, when some event occurs, or many times, once for each row affected by an INSERT, UPDATE, or DELETE statement. The trigger can be called after the event, to record it or take some followup action. Or, the trigger can be called before the event to prevent erroneous operations or fix new data so that it conforms to business rules. In Example 1-19 the table-level trigger fires whenever salaries in the employees table are updated, such as the processing in Example 1-7. For each update, the trigger writes a record to the emp_audit table.

CREATE TABLE emp_audit ( emp_audit_id NUMBER(6), up_date DATE, 
                         new_sal NUMBER(8,2), old_sal NUMBER(8,2) );

CREATE OR REPLACE TRIGGER audit_sal
   AFTER UPDATE OF salary ON employees FOR EACH ROW
BEGIN
-- bind variables are used here for values
   INSERT INTO emp_audit VALUES( :old.employee_id, SYSDATE, 
                                 :new.salary, :old.salary );
END;
/

The executable part of a trigger can contain procedural statements as well as SQL data manipulation statements. Besides table-level triggers, there are instead-of triggers for views and system-event triggers for schemas. For more information on triggers, see Oracle Database Concepts and Oracle Database Application Developer's Guide - Fundamentals. For information on the CREATE TRIGGER SQL statement, see Oracle Database SQL Reference.