PLSQL Tutorial

PL/SQL TUTORIAL Doan Quang MinhApril 10, 2012 CTI Cosatech VN

About this slide This Oracle PL/SQL tutorial guides you the basics of programming in PL/SQL with appropriate examples. You can use this tutorial as your reference while programming with PL/SQL. You should have basic knowledge about SQL and database management before reading this. 2

Agenda I. Introduction (5 minutes) II. Basic syntax (15 minutes) III. Advanced syntax (30 minutes) IV. Conclusion (2 minutes) V. Reference (2 minutes) VI. Keywords (3 minutes) VII. Q&A 3

I. Introduction 1. Introduction to PL/SQL  What is PL/SQL?  The PL/SQL Engine 2. Advantages of PL/SQL  Block Structures  Procedural Language Capability  Better Performance  Error Handling 4

1. Introduction to PL/SQL What is PL/SQL?  Procedural Language extension of SQL.  PL/SQL is a combination of SQL along with the procedural features of programming languages. It was developed by Oracle Corporation in the early 90’s to enhance the capabilities of SQL. 5 I. Introduction

1. Introduction to PL/SQL(cont) The PL/SQL Engine  Oracle uses a PL/SQL engine to processes the PL/SQL statements.  A PL/SQL code can be stored in the client system (client-side) or in the database (server-side). 6 I. Introduction

2. Advantages of PL/SQL  Block Structures: PL SQL consists of blocks of code, which can be nested within each other. Each block forms a unit of a task or a logical module. PL/SQL Blocks can be stored in the database and reused.  Procedural Language Capability: PL SQL consists of procedural language constructs such as conditional statements (if else statements) and loops like (FOR loops). 7 I. Introduction

2. Advantages of PL/SQL(cont)  Better Performance: PL SQL engine processes multiple SQL statements simultaneously as a single block, thereby reducing network traffic.  Error Handling: PL/SQL handles errors or exceptions effectively during the execution of a PL/SQL program. Once an exception is caught, specific actions can be taken depending upon the type of the exception or it can be displayed to the user with a message. 8 I. Introduction

II. Basic syntax 1. Block Structures 2. Operators 3. Comments 4. Delimiters 5. Variables 6. Constants 7. Records 8. Conditional Statements 9. Iterative Statements 9

1. Block Structures  Basic block [DECLARE] Variable declaration BEGIN Program Execution [EXCEPTION] Exception handling END; 10 II. Basic syntax  Example SET SERVEROUTPUT ON SIZE 1000000 BEGIN dbms_output.put_line('Hello PL/SQL'); END;

2. Operators  Comparison operators NOT IS NULL LIKE BETWEEN IN AND OR + - * / @ ; = <> != || <= >=  Assignment operator := (You can assign values to a variable, literal value, or function call but NOT a table column) 11 II. Basic syntax

3. Comments  Comment -- comment /* comment */  Example DECLARE /* Multi-line comments are not required to actually use multiple lines. */ BEGIN -- This is a single line comment NULL; END; 12 II. Basic syntax

4. Delimiters  Delimiter Item separator . Character string delimiter ' Quoted String delimiter " Bind variable indicator : Attribute indicator % Statement terminator ;  Example job_record.jobname := 'Test Job'; v_empno emp.empno%TYPE := &empno; 13 II. Basic syntax

5. Variables  Variable variable_name datatype [NOT NULL := value ];  Example DECLARE v_first_name VARCHAR2(20); v_employee_id NUMBER NOT NULL; v_last_name EMPLOYEES.LAST_NAME%TYPE; v_employee EMPLOYEES%ROWTYPE; v_hire_date DATE; BEGIN NULL; END; 14 II. Basic syntax

6. Constants  Constant constant_name CONSTANT datatype := VALUE;  Example DECLARE c_boss CONSTANT VARCHAR2(4) := ‘BOSS’; BEGIN NULL; END; 15 II. Basic syntax

7. Records  Record TYPE record_type_name IS RECORD( first_col_name column_datatype, second_col_name column_datatype, ...); record_name record_type_name;  Example DECLARE TYPE employee IS RECORD( v_employee_id NUMBER NOT NULL ,v_first_name VARCHAR2(20)); v_employee employee; BEGIN NULL; END; 16 II. Basic syntax

8. Conditional Statements  If statement IF condition THEN statement 1; ELSE statement 2; END IF; 17 II. Basic syntax  Example IF v_employee.sal > 0 THEN v_employee.sal := 1; ELSE v_employee.sal := 0; END IF;

9. Iterative Statements  Iterative statement LOOP statements; EXIT WHEN condition; (EXIT;) END LOOP; WHILE <condition> LOOP statements; END LOOP; FOR counter IN val1..val2 LOOP statements; END LOOP; 18 II. Basic syntax  Example LOOP monthly_val := daily_val * 31; EXIT WHEN monthly_value > 4000; END LOOP; WHILE monthly_val <= 4000 LOOP monthly_val := daily_val * 31; END LOOP; FOR counter IN 1..9 LOOP monthly_val := daily_val * 31; END LOOP;

III. Advanced syntax 1. Cursors 2. Explicit Cursors 3. Procedures 4. Functions 5. Parameters-Procedure, Function 6. Exception Handling 7. Triggers 19

1. Cursors  What is cursor ?  In memory work area  Store rows selected from DB  Process one row per time only  Active set is the set of rows the cursor hold.  Supported attributes  %FOUND  %NOTFOUND  %ROWCOUNT  %ISOPEN 20 III. Advanced

1. Cursors(cont)  Two types of cursors in PL/SQL  Implicit cursors  Explicit cursors  Implicit cursors These are created by default when DML statements like, INSERT, UPDATE, and DELETE statements are executed. They are also created when a SELECT statement that returns just one row is executed. 21 III. Advanced

1. Cursors(cont)  Example DECLARE v_rows number(5); BEGIN UPDATE employee SET salary = salary + 1000; IF SQL%NOTFOUND THEN dbms_output.put_line('None of the salaries where updated'); ELSIF SQL%FOUND THEN v_rows := SQL%ROWCOUNT; dbms_output.put_line('Salaries for ' || v_rows || 'employees are updated'); END IF; END; 22 III. Advanced

2. Explicit Cursors  What is explicit cursor ? An explicit cursor is defined in the declaration section of the PL/SQL Block. It is created on a SELECT Statement which returns more than one row. We can provide a suitable name for the cursor.  How to use explicit cursors ?  DECLARE the cursor in the declaration section.  OPEN the cursor in the Execution Section.  FETCH the data from cursor into PL/SQL variables or records in the Execution Section.  CLOSE the cursor in the Execution Section before you end the PL/SQL Block. 23 III. Advanced

2. Explicit Cursors  Example  Declaring a cursor DECLARE CURSOR emp_cur IS SELECT * FROM emp_tbl WHERE salary > 5000; 24 III. Advanced  Accessing the cursor BEGIN OPEN emp_cur; FETCH emp_cur INTO v_record; process_one_record(v_record); CLOSE emp_cur; END;

3. Procedures  What is procedures ?  A named PL/SQL block  A procedure has a header and a body  May or may not return values  If stored on DBMS, we call it stored procedures 25 III. Advanced

3. Procedures(cont)  Declaration CREATE [OR REPLACE] PROCEDURE proc_name [list of parameters] IS Declaration section BEGIN Execution section EXCEPTION Exception section END;  Execution  From the SQL prompt : EXECUTE [or EXEC] procedure_name;  Within another procedure: procedure_name; 26 III. Advanced

3. Procedures(cont)  Example CREATE OR REPLACE PROCEDURE employer_details IS CURSOR emp_cur IS SELECT first_name, last_name, salary FROM emp_tbl; emp_rec emp_cur%ROWTYPE; BEGIN FOR emp_rec IN sales_cur LOOP dbms_output.put_line(emp_cur.first_name); END LOOP; END; EXECUTE employer_details; 27 III. Advanced

4. Functions  What is functions?  A named PL/SQL block  A function has a header and a body  Must always return a value (different to a procedure)  If stored on DBMS, we call it stored functions 28 III. Advanced

4. Functions(cont)  Declaration CREATE [OR REPLACE] FUNCTION function_name [parameters] RETURN return_datatype; IS Declaration_section BEGIN Execution_section Return return_variable; EXCEPTION exception section Return return_variable; END; 29 III. Advanced

4. Functions(cont)  Execution  Since a function returns a value we can assign it to a variable variable_name := function_name;  As a part of a SELECT statement SELECT function_name FROM table;  In a PL/SQL Statements like, dbms_output.put_line(function_name); 30 III. Advanced

4. Functions(cont)  Example CREATE OR REPLACE FUNCTION employer_details_func RETURN VARCHAR(20); IS emp_name VARCHAR(20); BEGIN SELECT first_name INTO emp_name FROM emp_tbl WHERE empID = '100'; RETURN emp_name; END; SELECT employer_details_func FROM dual; 31 III. Advanced

5. Parameters in Procedure, Functions  3 ways to pass parameters  IN-parameters  OUT-parameters  IN OUT-parameters NOTE: If a parameter is not explicitly defined a parameter type, then by default it is an IN type parameter. 32 III. Advanced

5. Parameters in Procedure, Functions  Example CREATE OR REPLACE PROCEDURE emp_name ( p_id IN NUMBER , p_emp_name OUT VARCHAR2(20)) IS BEGIN SELECT first_name INTO p_emp_name FROM emp_tbl WHERE empID = p_id; END; 33 III. Advanced

6. Exception Handling 34 III. Advanced  What is a exception handling?  A feature to handle the Exceptions which occur in a PL/SQL Block  Avoid the source code from exiting abruptly  When an exception occurs a messages which explains its cause is received  3 parts of an PL/SQL exception? • Type of Exception • An Error Code • A message

6. Exception Handling 35 III. Advanced  Structure of Exception Handling EXCEPTION WHEN ex_name1 THEN -- Error handling statements WHEN ex_name2 THEN -- Error handling statements WHEN Others THEN -- Error handling statements

6. Exception Handling 36 III. Advanced  3 types of exception  Named System Exceptions  Unnamed System Exceptions  User-defined Exceptions

6. Exception Handling 37 III. Advanced  Example BEGIN -- Execution section EXCEPTION WHEN NO_DATA_FOUND THEN dbms_output.put_line ('A SELECT...INTO did not return any row.'); END;

7. Triggers  What is a Trigger? A trigger is a pl/sql block structure which is fired when a DML statements like Insert, Delete, Update is executed on a database table. A trigger is triggered automatically when an associated DML statement is executed. 38 III. Advanced

7. Triggers(cont)  How to create a trigger? CREATE [OR REPLACE ] TRIGGER trigger_name {BEFORE | AFTER | INSTEAD OF } {INSERT [OR] | UPDATE [OR] | DELETE} [OF col_name] ON table_name [REFERENCING OLD AS o NEW AS n] [FOR EACH ROW] WHEN (condition) BEGIN --- sql statements END; 39 III. Advanced

7. Triggers(cont)  Example The price of a product changes constantly. It is important to maintain the history of the prices of the products. We can create a trigger to update the 'product_price_history' table when the price of the product is updated in the 'product' table. 1. Create the 'product' table and 'product_price_history' table 40 III. Advanced CREATE TABLE product_price_history (product_id NUMBER(5) ,product_name VARCHAR2(32) ,supplier_name VARCHAR2(32) ,unit_price NUMBER(7,2) ); CREATE TABLE product (product_id NUMBER(5) ,product_name VARCHAR2(32) ,supplier_name VARCHAR2(32) ,unit_price NUMBER(7,2) );

7. Triggers(cont)  Example(cont) 2. Create the price_history_trigger and execute it. 41 III. Advanced CREATE OR REPLACE TRIGGER price_history_trigger BEFORE UPDATE OF unit_price ON product FOR EACH ROW BEGIN INSERT INTO product_price_history VALUES (:old.product_id, :old.product_name, :old.supplier_name, :old.unit_price); END;

7. Triggers(cont)  Example(cont) 3. Lets update the price of a product. -- Once executed, the trigger fires and updates the -- product_price_history' table UPDATE PRODUCT SET unit_price = 800 WHERE product_id = 100 4. If you ROLLBACK the transaction before committing to the database, the data inserted to the table is also rolled back. 42 III. Advanced

7. Triggers(cont)  Types of PL/SQL Triggers  Row level trigger - An event is triggered for each row updated, inserted or deleted  Statement level trigger - An event is triggered for each SQL statement executed  PL/SQL Trigger Execution Hierarchy  BEFORE statement trigger fires first  Next BEFORE row level trigger fires, once for each row affected  Then AFTER row level trigger fires once for each affected row. This events will alternates between BEFORE and AFTER row level triggers  Finally the AFTER statement level trigger fires 43 III. Advanced

7. Triggers(cont)  How To know Information about Triggers.  We can use the data dictionary view 'USER_TRIGGERS' to obtain information about any trigger. DESC USER_TRIGGERS;  This view stores information about header and body of the trigger SELECT * FROM user_triggers WHERE trigger_name = 'trigger_name';  You can drop a trigger using the following command. DROP TRIGGER trigger_name; 44 III. Advanced

IV. Conclusion 45 Now, I hope this slide gave you some ideas about working with PL/SQL. Please let me know if there’s any mistake or issue in the tutorial. All comments are welcome. With our position in CTI Vietnam. This amount of knowledge would not be enough for us. There’re many more topics we need to invest our time: performance tuning, data mining, coding convention, best practices, … So, let’s share our knowledge, TOGETHER.

V. Reference 46 1. PL/SQL Tutorial from plsql-tutorial.com 2. PL/SQL User's Guide and Reference, Release 2 (9.2), from Oracle 3. Database Interaction with PL/SQL, Jagadish Chatarji (Dev Shed) 4. PL/SQL Code Examples, ACS department, University of Utah 5. Doing SQL from PL/SQL: Best and Worst Practices, Oracle

VI. Keywords 47 Below is some keywords not mentioned in this slide. If possible, you should google them. General: Embedded SQL, Native dynamic SQL, The DBMS_Sql API, Name resolution, PL/SQL compiler, bounded and unbounded, oracle hint, materialized view. Cursors: sharable SQL structure, session cursor, ref cursor, cursor variable, strong ref cursor, weak ref cursor, identified cursor, DBMS_Sql numeric cursor. Exception Handling: RAISE_APPLICATION_ERROR, PRAGMA, EXCEPTION_INIT. Triggers: CYCLIC CASCADING, ROLLBACK, INSTEAD OF, REFERENCING OLD.

VII. Q&A 48 Questions, please ...

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