Introduction to PLSQL Objectives After completing this lesson

Introduction to PL/SQL

Objectives After completing this lesson, you should be able to do the following: Explain the need for PL/SQL Explain the benefits of PL/SQL Identify the different types of PL/SQL blocks Output messages in PL/SQL

About PL/SQL: Stands for “Procedural Language extension to SQL” Is Oracle Corporation’s standard data access language for relational databases Seamlessly integrates procedural constructs with SQL

About PL/SQL: Provides a block structure for executable units of code. Maintenance of code is made easier with such a welldefined structure. Provides procedural constructs such as: Variables, constants, and data types Control structures such as conditional statements and loops Reusable program units that are written once and executed many times

PL/SQL Environment PL/SQL engine PL/SQL block procedural SQL Procedural statement executor SQL statement executor Oracle database server

Benefits of PL/SQL Integration of procedural constructs with SQL Improved performance SQL 1 SQL 2 … SQL IF. . . THEN SQL ELSE SQL END IF; SQL

Benefits of PL/SQL Modularized program development Integration with Oracle tools Portability Exception handling

PL/SQL Block Structure DECLARE (optional) BEGIN (mandatory) SQL statements PL/SQL statements EXCEPTION (optional) Variables, cursors, user-defined exceptions Actions to perform when errors occur END; (mandatory)

Block Types Anonymous Procedure Function [DECLARE] PROCEDURE name IS BEGIN --statements [EXCEPTION] FUNCTION name RETURN datatype IS BEGIN --statements RETURN value; [EXCEPTION] END;

Program Constructs Tools Constructs Database Server Constructs Anonymous blocks Application procedures or functions Stored procedures or functions Application packages Stored packages Application triggers Database triggers Object types

Create an Anonymous Block Enter the anonymous block in the SQL Developer workspace:

Execute an Anonymous Block Click the Run Script button to execute the anonymous block: Run Script

Test the Output of a PL/SQL Block Enable output in SQL Developer by clicking the Enable DBMS Output button on the DBMS Output tab: Enable DBMS Output Tab Use a predefined Oracle package and its procedure: DBMS_OUTPUT. PUT_LINE(' The First Name of the Employee is ' || f_name); …

Test the Output of a PL/SQL Block

Declaring PL/SQL Variables

Objectives After completing this lesson, you should be able to do the following: Recognize valid and invalid identifiers List the uses of variables Declare and initialize variables List and describe various data types Identify the benefits of using the %TYPE attribute Declare, use, and print bind variables

Use of Variables can be used for: Temporary storage of data Manipulation of stored values Reusability SELECT first_name, department_id INTO v_fname, v_deptno FROM … Jennifer 10 v_fname v_deptno

Requirements for Variable Names A variable name: Must start with a letter Can include letters or numbers Can include special characters (such as $, _, and # ) Must contain no more than 30 characters Must not include reserved words

Handling Variables in PL/SQL Variables are: Declared and initialized in the declarative section Used and assigned new values in the executable section Passed as parameters to PL/SQL subprograms Used to hold the output of a PL/SQL subprogram

Declaring and Initializing PL/SQL Variables Syntax: Examples: identifier [CONSTANT] datatype [NOT NULL] [: = | DEFAULT expr]; DECLARE v_hiredate v_deptno v_location c_comm DATE; NUMBER(2) NOT NULL : = 10; VARCHAR 2(13) : = 'Atlanta'; CONSTANT NUMBER : = 1400;

Declaring and Initializing PL/SQL Variables 1 2 DECLARE v_my. Name VARCHAR 2(20); BEGIN DBMS_OUTPUT. PUT_LINE('My name is: '|| v_my. Name); v_my. Name : = 'John'; DBMS_OUTPUT. PUT_LINE('My name is: '|| v_my. Name); END; / DECLARE v_my. Name VARCHAR 2(20): = 'John'; BEGIN v_my. Name : = 'Steven'; DBMS_OUTPUT. PUT_LINE('My name is: '|| v_my. Name); END; /

Delimiters in String Literals DECLARE v_event VARCHAR 2(15); BEGIN v_event : = q'!Father's day!'; DBMS_OUTPUT. PUT_LINE('3 rd Sunday in June is : '|| v_event ); v_event : = q'[Mother's day]'; DBMS_OUTPUT. PUT_LINE('2 nd Sunday in May is : '|| v_event ); END; /

Types of Variables PL/SQL variables: Scalar Composite Reference Large object (LOB) Non-PL/SQL variables: Bind variables

Types of Variables TRUE 25 -JAN-01 Snow White Long, long ago, in a land far, far away, there lived a princess called Snow White. . . 256120. 08 Atlanta

Guidelines for Declaring and Initializing PL/SQL Variables Follow naming conventions. Use meaningful identifiers for variables. Initialize variables designated as NOT NULL and CONSTANT. Initialize variables with the assignment operator (: =) or the DEFAULT keyword: v_my. Name VARCHAR 2(20): ='John'; v_my. Name VARCHAR 2(20) DEFAULT 'John'; Declare one identifier per line for better readability and code maintenance.

Guidelines for Declaring PL/SQL Variables Avoid using column names as identifiers. DECLARE employee_id NUMBER(6); BEGIN SELECT employee_id INTO employee_id FROM employees WHERE last_name = 'Kochhar'; END; / Use the NOT NULL constraint when the variable must hold a value.

Scalar Data Types Hold a single value Have no internal components TRUE 25 -JAN-01 The soul of the lazy man desires, and he has nothing; but the soul of the diligent shall be made rich. 256120. 08 Atlanta

Base Scalar Data Types CHAR [(maximum_length)] VARCHAR 2 (maximum_length) NUMBER [(precision, scale)] BINARY_INTEGER PLS_INTEGER BOOLEAN BINARY_FLOAT BINARY_DOUBLE

Base Scalar Data Types DATE TIMESTAMP WITH TIME ZONE TIMESTAMP WITH LOCAL TIME ZONE INTERVAL YEAR TO MONTH INTERVAL DAY TO SECOND

Declaring Scalar Variables Examples: DECLARE v_emp_job VARCHAR 2(9); v_count_loop BINARY_INTEGER : = 0; v_dept_total_sal NUMBER(9, 2) : = 0; v_orderdate DATE : = SYSDATE + 7; c_tax_rate CONSTANT NUMBER(3, 2) : = 8. 25; v_valid BOOLEAN NOT NULL : = TRUE; . . .

%TYPE Attribute Is used to declare a variable according to: A database column definition Another declared variable Is prefixed with: The database table and column The name of the declared variable

Declaring Variables with the %TYPE Attribute Syntax identifier table. column_name%TYPE; Examples . . . emp_lname. . . employees. last_name%TYPE; . . . balance min_balance. . . NUMBER(7, 2); balance%TYPE : = 1000;

Declaring Boolean Variables Only the TRUE, FALSE, and NULL values can be assigned to a Boolean variable. Conditional expressions use the logical operators AND and OR and the unary operator NOT to check the variable values. The variables always yield TRUE, FALSE, or NULL. Arithmetic, character, and date expressions can be used to return a Boolean value.

Bind Variables Bind variables are: Created in the environment Also called host variables Created with the VARIABLE keyword Used in SQL statements and PL/SQL blocks Accessed even after the PL/SQL block is executed Referenced with a preceding colon

Printing Bind Variables Example: VARIABLE b_emp_salary NUMBER BEGIN SELECT salary INTO : b_emp_salary FROM employees WHERE employee_id = 178; END; / PRINT b_emp_salary SELECT first_name, last_name FROM employees WHERE salary=: b_emp_salary;

Printing Bind Variables Example: VARIABLE b_emp_salary NUMBER SET AUTOPRINT ON DECLARE v_empno NUMBER(6): =&empno; BEGIN SELECT salary INTO : b_emp_salary FROM employees WHERE employee_id = v_empno; END; o Output: 7000

LOB Data Type Variables Book (CLOB) Photo (BLOB) Movie (BFILE) NCLOB

Composite Data Types TRUE 23 -DEC-98 PL/SQL table structure 1 2 3 4 SMITH JONES NANCY TIM VARCHAR 2 PLS_INTEGER ATLANTA PL/SQL table structure 1 2 3 4 5000 2345 12 3456 NUMBER PLS_INTEGER

Writing Executable Statements

Objectives After completing this lesson, you should be able to do the following: Identify lexical units in a PL/SQL block Use built-in SQL functions in PL/SQL Describe when implicit conversions take place and when explicit conversions have to be dealt with Write nested blocks and qualify variables with labels Write readable code with appropriate indentation Use sequences in PL/SQL expressions

Lexical Units in a PL/SQL Block Lexical units: Are building blocks of any PL/SQL block Are sequences of characters including letters, numerals, tabs, spaces, returns, and symbols Can be classified as: Identifiers: v_fname, c_percent Delimiters: ; , +, Literals: John, 428, True Comments: --, /* */

PL/SQL Block Syntax and Guidelines Literals Character and date literals must be enclosed in single quotation marks. Numbers can be simple values or in scientific notation. name : = 'Henderson'; Statements can span several lines. 1 2 3

Commenting Code Prefix single-line comments with two hyphens (--). Place multiple-line comments between the symbols /* and */. DECLARE Example: . . . v_annual_sal NUMBER (9, 2); BEGIN /* Compute the annual salary based on the monthly salary input from the user */ v_annual_sal : = monthly_sal * 12; --The following line displays the annual salary DBMS_OUTPUT. PUT_LINE(v_annual_sal); END; /

SQL Functions in PL/SQL Available in procedural statements: Single-row functions Not available in procedural statements: DECODE Group functions

SQL Functions in PL/SQL: Examples Get the length of a string: v_desc_size INTEGER(5); v_prod_description VARCHAR 2(70): ='You can use this product with your radios for higher frequency'; -- get the length of the string in prod_description v_desc_size: = LENGTH(prod_description); Get the number of months an employee has worked: v_tenure: = MONTHS_BETWEEN (CURRENT_DATE, v_hiredate);

Using Sequences in PL/SQL Expressions Starting in 11 g: DECLARE v_new_id NUMBER; BEGIN v_new_id : = my_seq. NEXTVAL; END; / Before 11 g: DECLARE v_new_id NUMBER; BEGIN SELECT my_seq. NEXTVAL INTO v_new_id FROM Dual; END; /

Data Type Conversion Converts data to comparable data types Is of two types: Implicit conversion Explicit conversion Functions: TO_CHAR TO_DATE TO_NUMBER TO_TIMESTAMP

Data Type Conversion 1 date_of_joining DATE: = '02 -Feb-2000'; 2 date_of_joining DATE: = 'February 02, 2000'; 3 date_of_joining DATE: = TO_DATE('February 02, 2000', 'Month DD, YYYY');

Nested Blocks PL/SQL blocks can be nested. An executable section (BEGIN … END) can contain nested blocks. An exception section can contain nested blocks.

Nested Blocks o o o DECLARE Example: v_outer_variable VARCHAR 2(20): ='GLOBAL VARIABLE'; BEGIN DECLARE v_inner_variable VARCHAR 2(20): ='LOCAL VARIABLE'; BEGIN DBMS_OUTPUT. PUT_LINE(v_inner_variable); DBMS_OUTPUT. PUT_LINE(v_outer_variable); END;

Variable Scope and Visibility o o o o 1 o o o 2 o o DECLARE v_father_name VARCHAR 2(20): ='Patrick'; v_date_of_birth DATE: ='20 -Apr-1972'; BEGIN DECLARE v_child_name VARCHAR 2(20): ='Mike'; v_date_of_birth DATE: ='12 -Dec-2002'; BEGIN DBMS_OUTPUT. PUT_LINE('Father''s Name: '||v_father_name); DBMS_OUTPUT. PUT_LINE('Date of Birth: '||v_date_of_birth); DBMS_OUTPUT. PUT_LINE('Child''s Name: '||v_child_name); END; DBMS_OUTPUT. PUT_LINE('Date of Birth: '||v_date_of_birth); END; /

Qualify an Identifier o o o o o BEGIN <<outer>> DECLARE v_father_name VARCHAR 2(20): ='Patrick'; v_date_of_birth DATE: ='20 -Apr-1972'; BEGIN DECLARE v_child_name VARCHAR 2(20): ='Mike'; v_date_of_birth DATE: ='12 -Dec-2002'; BEGIN DBMS_OUTPUT. PUT_LINE('Father''s Name: '||v_father_name); DBMS_OUTPUT. PUT_LINE('Date of Birth: ' ||outer. v_date_of_birth); DBMS_OUTPUT. PUT_LINE('Child''s Name: '||v_child_name); DBMS_OUTPUT. PUT_LINE('Date of Birth: '||v_date_of_birth); END; END outer;

Quiz: Determining Variable Scope 1 2 BEGIN <<outer>> DECLARE v_sal NUMBER(7, 2) : = 60000; v_comm NUMBER(7, 2) : = v_sal * 0. 20; v_message VARCHAR 2(255) : = ' eligible for commission'; BEGIN DECLARE v_sal NUMBER(7, 2) : = 50000; v_comm NUMBER(7, 2) : = 0; v_total_comp NUMBER(7, 2) : = v_sal + v_comm; BEGIN v_message : = 'CLERK not'||v_message; outer. v_comm : = v_sal * 0. 30; END; v_message : = 'SALESMAN'||v_message; END outer; /

Operators in PL/SQL } Logical Arithmetic Concatenation Parentheses to control order of operations Exponential operator (**) Same as in SQL

Operators in PL/SQL: Examples Increment the counter for a loop_count : = loop_count + 1; Set the value of a Boolean flag. good_sal : = sal BETWEEN 50000 AND 150000; Validate whether an employee number contains a value. valid : = (empno IS NOT NULL);

Programming Guidelines Make code maintenance easier by: Documenting code with comments Developing a case convention for the code Developing naming conventions for identifiers and other objects Enhancing readability by indenting

Indenting Code For clarity, indent each level of code. BEGIN IF x=0 THEN y: =1; END IF; END; / DECLARE deptno NUMBER(4); location_id NUMBER(4); BEGIN SELECT department_id, location_id INTO deptno, location_id FROM departments WHERE department_name = 'Sales'; . . . END; /

Interacting with the Oracle Database Server

Objectives After completing this lesson, you should be able to do the following: Determine the SQL statements that can be directly included in a PL/SQL executable block Manipulate data with DML statements in PL/SQL Use transaction control statements in PL/SQL Make use of the INTO clause to hold the values returned by a SQL statement Differentiate between implicit cursors and explicit cursors Use SQL cursor attributes

SQL Statements in PL/SQL Retrieve a row from the database by using the SELECT command. Make changes to rows in the database by using DML commands. Control a transaction with the COMMIT, ROLLBACK, or SAVEPOINT command.

SELECT Statements in PL/SQL Retrieve data from the database with a SELECT statement. Syntax: SELECT INTO FROM [WHERE select_list {variable_name[, variable_name]. . . | record_name} table condition];

SELECT Statements in PL/SQL The INTO clause is required. Queries must return only one row. Example: DECLARE v_fname VARCHAR 2(25); BEGIN SELECT first_name INTO v_fname FROM employees WHERE employee_id=200; DBMS_OUTPUT. PUT_LINE(' First Name is : '||v_fname); END; /

Retrieving Data in PL/SQL Retrieve hire_date and salary for the specified employee. Example: DECLARE v_emp_hiredate employees. hire_date%TYPE; v_emp_salary employees. salary%TYPE; BEGIN SELECT hire_date, salary INTO v_emp_hiredate, v_emp_salary FROM employees WHERE employee_id = 100; END; /

Retrieving Data in PL/SQL Return the sum of the salaries for all the employees in the specified department. Example: DECLARE v_sum_sal NUMBER(10, 2); v_deptno NUMBER NOT NULL : = 60; BEGIN SELECT SUM(salary) -- group function INTO v_sum_sal FROM employees WHERE department_id = v_deptno; DBMS_OUTPUT. PUT_LINE ('The sum of salary is ' || v_sum_sal); END;

Naming Conventions DECLARE hire_date employees. hire_date%TYPE; sysdate hire_date%TYPE; employee_id employees. employee_id%TYPE : = 176; BEGIN SELECT hire_date, sysdate INTO hire_date, sysdate FROM employees WHERE employee_id = employee_id; END; /

Naming Conventions Use a naming convention to avoid ambiguity in the WHERE clause. Avoid using database column names as identifiers. Syntax errors can arise because PL/SQL checks the database first for a column in the table. The names of local variables and formal parameters take precedence over the names of database tables. The names of database table columns take precedence over the names of local variables.

Using PL/SQL to Manipulate Data Make changes to database tables by using DML commands: INSERT UPDATE DELETE MERGE DELETE INSERT UPDATE MERGE

Inserting Data Add new employee information to the EMPLOYEES table. BEGIN INSERT Example: INTO employees (employee_id, first_name, last_name, email, hire_date, job_id, salary) VALUES(employees_seq. NEXTVAL, 'Ruth', 'Cores', 'RCORES', CURRENT_DATE, 'AD_ASST', 4000); END; /

Updating Data Increase the salary of all employees who are stock clerks. DECLARE Example: sal_increase employees. salary%TYPE : = 800; BEGIN UPDATE employees SET salary = salary + sal_increase WHERE job_id = 'ST_CLERK'; END; /

Deleting Data Delete rows that belong to department 10 from the employees table. DECLARE Example: deptno employees. department_id%TYPE : = 10; BEGIN DELETE FROM employees WHERE department_id = deptno; END; /

Merging Rows Insert or update rows in the copy_emp table to match the employees table. BEGIN MERGE INTO copy_emp c USING employees e ON (e. employee_id = c. empno) WHEN MATCHED THEN UPDATE SET c. first_name = e. first_name, c. last_name = e. last_name, c. email = e. email, . . . WHEN NOT MATCHED THEN INSERT VALUES(e. employee_id, e. first_name, e. last_name, . . . , e. department_id); END; /

SQL Cursor A cursor is a pointer to the private memory area allocated by the Oracle server. A cursor is used to handle the result set of a SELECT statement. There are two types of cursors: Implicit: Created and managed internally by the Oracle server to process SQL statements Explicit: Declared explicitly by the programmer

SQL Cursor Attributes for Implicit Cursors Using SQL cursor attributes, you can test the outcome of your SQL statements. SQL%FOUND Boolean attribute that evaluates to TRUE if the most recent SQL statement returned at least one row SQL%NOTFO Boolean attribute that evaluates to TRUE UND if the most recent SQL statement did not return even one row SQL%ROWCO An integer value that represents the UNT number of rows affected by the most recent SQL statement

SQL Cursor Attributes for Implicit Cursors Delete rows that have the specified employee ID from the employees table. Print the number of rows deleted. DECLARE Example: v_rows_deleted VARCHAR 2(30) v_empno employees. employee_id%TYPE : = 176; BEGIN DELETE FROM employees WHERE employee_id = v_empno; v_rows_deleted : = (SQL%ROWCOUNT || ' row deleted. '); DBMS_OUTPUT. PUT_LINE (v_rows_deleted); END;