Database Programming: Overview Contents 1. The Impedance Mismatch 2. JDBC 1. From the Elmasri/Navathe text 2. From the ASU scholars 3. PLSQL: by Prof. James Dullea, VU Slide 1 of 36

The Impedance Mismatch It’s the disconnect between the approach of a database language and that of a conventional programming language in which it’s embedded: the former uses tables (sets of rows), while the latter uses a record at a time. Note how each of JDBC and PL/SQL addresses this. Slide 2 of 36

Next up: JDBC From the Elmasri/Navathe text From the ASU scholars Slide 3 of 36

Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Chapter 9 Introduction to SQL Programming Techniques

Slide 9- 5 Java Database Connectivity JDBC: SQL connection function calls for Java programming A Java program with JDBC functions can access any relational DBMS that has a JDBC driver JDBC allows a program to connect to several databases (known as data sources)

Slide 9- 6 Steps in JDBC Database Access 1.Import JDBC library (java.sql.*) 2.Load JDBC driver: Class.forname(“oracle.jdbc.driver.OracleDrive r”) 3.Define appropriate variables 4.Create a connect object (via getConnection ) 5.Create a statement object from the Statement class: 1. PreparedStatment2. CallableStatement 6.Identify statement parameters (designated by question marks) 7.Bound parameters to program variables 8.Execute SQL statement (referenced by an object) via JDBC’s executeQuery 9.Process query results (returned in an object of type ResultSet) ResultSet is a 2-dimentional table

Slide 9- 7 Embedded SQL in Java: An Example ssn = readEntry("Enter a SSN: "); try { #sql{select FNAME< LNAME, ADDRESS, SALARY into :fname, :lname, :address, :salary from EMPLOYEE where SSN = :ssn}; } catch (SQLException se) { System.out.println("SSN does not exist: ",+ssn); return; } System.out.println(fname + " " + lname + … );

WEB/DB 8 ADVANCED DATABASE CONCEPTS JDBC Susan D. Urban and Suzanne W. Dietrich Department of Computer Science and Engineering Arizona State University Tempe, AZ

WEB/DB 9 OPEN DATABASE CONNECTIVITY (ODBC) Standard application programming interface (API) for accessing a database. A separate module or driver is required for each database to be accessed. Based on the standard Call Level Interface (CLI) of the SQL Access Group (part of the X/Open Standard). Can use the API to execute SQL statements, update tables, and retrieve metadata.

WEB/DB 10 ODBC ISSUES IN A JAVA ENVIRONMENT ODBC uses C to access the data source. This poses issues with implementation. Hence, it cannot be used in conjunction with Java. OBDC’S API cannot be used by translating the API to Java since there is no pointer concept in Java. ODBC requires the driver manager to be installed on every client installation.

WEB/DB 11 JAVA DATABASE CONNECTIVITY (JDBC) Java API for connecting programs written in Java to databases. Based on ODBC. Allows Java programs to send SQL statements to any relational database. Platform independent. JDBC drivers written in Java can be accessed from any computer in a heterogeneous network. A JDBC-ODBC bridge can be used to access databases using the ODBC interface.

WEB/DB 12 TWO-TIER JDBC ARCHITECTURES Java application or applet talks directly to the data source. Client sends requests to the server through user interfaces. JDBC Driver communicates with the data source to access the data. Sun Microsystems Inc. 1999

WEB/DB 13 THREE-TIER JDBC ARCHITECTURES Uses a third tier between the client and the server. Controls updates that are made to the database. Secure and robust. Sun Microsystems Inc. 1999

WEB/DB 14 DEVELOPING JDBC APPLICATIONS Import JDBC classes (java.sql.*) Load the JDBC Driver. Connect to the database. Use the JDBC API to access the database. Disconnect from the database.

WEB/DB 15 ESTABLISHING A CONNECTION TO A DATABASE The first step in accessing data from any relational database using JDBC is to establish a connection with the data source. The Connection object is used to get meta data and execute SQL statements. The getConnection method returns a Connection object that represents a session with a specific database. The parameters in the getConnection method are URL, username and password. Username and password are optional. The URL consists of the protocol “jdbc”, sub- protocol “odbc”, and the Data Source Name (DSN).

WEB/DB 16 EXAMPLE TO CONNECT TO A DATABASE /* dbName is the registered name of the ODBC data source */ String url = "jdbc:odbc:" + dbName ; try { /* Load the jdbc-odbc driver */ Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); /* Open a connection to the odbc data source */ con =DriverManager.getConnection(url,"",""); }

WEB/DB 17 STATEMENTS A Statement Object is used to send SQL queries to a database. A Statement object should be created using the connection method createStatement().

WEB/DB 18 TYPES OF STATEMENTS There are three types of statement objects: Simple statements Used to execute SQL statements without any parameters. Statement stmt = connection.createStatement(); Prepared Statements Used when a statement will be called several times and is stored as a pre-compiled statement with IN parameters. PreparedStatement pstmt = con.prepareStatement(“update employee set salary=? where ssn=?”); Callable Statements Used with calls to database stored procedures and SQL statements with OUT parameters.

WEB/DB 19 EXECUTING SIMPLE STATEMENTS The execution of a statement returns results into a ResultSet object. The ResultSet object is then used to access query results. ResultSet rs = null; The executeQuery() method is used to execute an SQL statement through the statement object. rs = stmt.executeQuery("SELECT a, b, c FROM Table1"); The close() method is used to close the ResultSet. rs.close();

WEB/DB 20 GETTING DATA FROM A ResultSet The next() method is used to traverse through tuples in the ResultSet object. The data stored in a ResultSet object is retrieved through a set of get methods that allows access to the various columns of the current row. The results are printed out on a screen using the Servlet output stream. while(rs.next()) { out.println(rs.getString(“SSN”)); }

WEB/DB 21 DATABASE METADATA Metadata is the information in the database that is associated with the database schema: Table names Column names Column types The metadata associated with a database can be queried using JDBC. The metadata associated with the result set object of a statement execution can also be queried.

WEB/DB 22 DATABASE METADATA RETRIEVAL Create a metadata object. DatabaseMetaData dbmd ; Retrieve metadata from the database through the connection established. dbmd = con.getMetaData(); The getTables() method of the metadata object is used to retrieve information about the tables in a database. The information is stored in a result set object. ResultSet rsTables = dbmd.getTables(null, null, null, null);

WEB/DB 23 GETTING THE METADATA The getString() method of the ResultSet object is used to locate a specific table. String tableName = rsTables.getString("TABLE_NAME"); The getColumns() method is used to retrieve information about the columns and column types in a table, with the results stored in a ResultSet object. ResultSet rsColumns = dbmd.getColumns(null,null,tableName,null); while (rsColumns.next()) { … }

Next up: PL/SQL By Prof. James Dullea Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 24 of 36

Dr. James Dullea, CSC8490 Introduction to PL/SQLSlide 25 of 36 7From Prof. Dullea CSC8490 Introduction to PL/SQL Module 01-9 Revised: June 12, 2005 Dr. James Dullea

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 26 of 36 Introduction to PL/SQL What is PL/SQL Why PL/SQL Kinds of PL/SQL BLOCKS Anonymous or Named Blocks Named Blocks (Stored procedures, Funtions, Triggers) Exceptions Assignments (2)

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 27 of 36 What is PL/SQL PL/SQL is a sophistical programming language used to access an Oracle database from a various environments. PL/SQL stands for Procedural Language/SQL. It extends SQL by adding constructs found in other procedural languages, such as: loops, conditional statements, declared variables, accessing individual records one at a time, and many others.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 28 of 36 Why use PL/SQL Compared to SQL, PL/SQL has the procedural constructs that are useful to express a desired process from start to end. One block of PL/SQL code can bundled several SQL statements together as a single unit. Making less network traffic and improving application performance. PL/SQL can be integrated with other languages, such as Java, to take advantage of the strongest features of both languages.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 29 of 36 Kinds of PL/SQL BLOCKS The basic unit in any PL/SQL PROGRAM is a BLOCK. All PL/SQL programs are composed of a single block or blocks that occur either sequentially or nested within another block. There are two kinds of blocks: Anonymous blocks are generally constructed dynamically and executed only once by the user. It is sort of a complex SQL statement. Named blocks are blocks that have a name associated with them, are stored in the database, and can be executed again and again, can take in parameters, and can modify and existing database.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 30 of 36 Structure of Anonymous Block DECLARE /* Declare section (optional). */ BEGIN /* Executable section (required). */ EXCEPTION /* Exception handling section (optional). */ END; -- end the block (do not forget the “ ; “ in the end.) /

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 31 of 36 Example of Anonymous Block SET SERVEROUTPUT ON DECLARE v_last_name VARCHAR2(15); v_salary employee.salary%TYPE; CURSOR c_query IS SELECT lname, salary FROM employee; BEGIN OPEN c_query; LOOP FETCH c_query INTO v_last_name, v_salary; IF v_salary >= THEN DBMS_OUTPUT.PUT_LINE (v_last_name||' '||v_salary); END IF; EXIT WHEN c_query%NOTFOUND; END LOOP; CLOSE c_query; END; /

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 32 of 36 PL/SQL Build-In Utility Packages DBMS_OUTPUT.PUT_LINE SET SERVEROUTPUT ON to allow output to be displayed to the screen DBMS_OUTPUT.PUT_LINE Usage: DBMS_OUTPUT.PUT_LINE ( Argument ) Argument tendS to resemble the concatenated arguments of the SELECT clause in an SQL query. If the argument is not initialized, then a NULL VALUE will be displayed.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 33 of 36 PL/SQL Build-In Utility Packages Example SET SERVEROUTPUT ON DECLARE v_name VARCHAR2(30); v_title VARCHAR2(20); BEGIN v_name := 'James Dullea'; v_title := 'Research Scientist'; DBMS_OUTPUT.PUT_LINE(v_name||' works as a '||v_title); END; /

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 34 of 36 Variables and Types A variable is a storage location that can be read from or assigned to by the program. It is declared in the declarative section within a PL/SQL block. v_last_name VARCHAR2(15); Every variable has a specific data type associated with it. Variables can be associated with a table structure. v_salary employee.salary%TYPE;

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 35 of 36 Data Types Scalar type Numeric: INT, DEC,NUMBER,BINARY_INTEGER … Character: CHAR, CHARACTER, STRING, VARCHAR, VARCHAR2… Boolean: TRUE, FALSE. Date: DATE Composite types RECORD, TABLE, VARRAY Reference types CURSORS, OBJECT TYPES Lob types BFILE, LOB, CLOB, NLOB

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 36 of 36 CURSORS  A cursor is used to process a single row 'at a time' from multiple rows retrieved from the database.  Cursors are declared in the Declaration Section. CURSOR c_query IS SELECT lname, salary FROM employee;  The cursor can be declared for complex queries involving joins and conditions.  Cursors must be OPENed to be accessed and CLOSEd before ending the program. OPEN c_query; CLOSE c_query;

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 37 of 36 CURSORS  The FETCH statement is used to retrieve the output of a single record from the CURSOR SELECT statement INTO associate variables. FETCH c_query INTO v_last_name, v_salary;  Cursors can be opened and closed more than once in a block and if the a WHERE statement exists, the values of the binding variables can be modified.  “Cursor FOR loop” is a special type of for loop which the SQL cursor operations are carried out implicitly.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 38 of 36 Conditional Statements Conditional Processing The specified conditions are evaluated by the system and the result determines which sequence of statements is to be carried out. IF THEN END IF; IF THEN ELSE END IF;

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 39 of 36 Conditional Statements (ELSIF) IF THEN ELSIF THEN ELSIF THEN ELSIF THEN ELSE END IF;

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 40 of 36 Loop Structures  Unconstrained loops  WHILE loop  FOR loop  GOTO >

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 41 of 36 Unconstrained Loops LOOP EXIT WHEN END LOOP;

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 42 of 36 WHILE LOOP WHILE LOOP END LOOP; Note: The loop will continue to process as long as the condition is TRUE or an EXIT (or EXIT WHEN) statement is encountered.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 43 of 36 FOR LOOP FOR IN [REVERSE].. LOOP END LOOP;

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 44 of 36 GOTO statement GOTO label; The label is defined in the block by being enclosed in double angle brackets. Example: LOOP IF THEN GOTO get_out_of_loop; END LOOP; >

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 45 of 36 NAMED BLOCKS The following are types of NAMED BLOCKS Stored Procedures Similar to an anonymous block except it can be stored in the database, can accept parameters, and can be executed over and over again (with different parameters) Functions Type of named blocks that is executed within a DML or SQL statement. It may take in one or more parameters and RETURNs only one value back to the calling application. Triggers A named block that executes only when an associated DML statement is executed, such as an INSERT, UPDATE, or DELETE statement.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 46 of 36 Block Structure for PL/SQL Subprograms (Procedures or Functions) Program Comments (optional) Header (mandatory) IS|AS (mandatory) Declaration Section BEGIN (mandatory) Executable Section EXCEPTION (optional) Exception Section END; (mandatory) /

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 47 of 36 Block Structure for PL/SQL subprograms Completed procedure example CREATE OR REPLACE PROCEDURE AddDepartment /*Procedure to add rows In the COMPANY.department table */ (p_DepartmentName IN department.dname%TYPE, p_DepartmentNumber IN department.dnumber%TYPE, p_DepartmentManager IN department.mgrssn%TYPE, p_ManagerStartDate IN department.mgrstartdate%TYPE) AS BEGIN INSERT INTO DEPARTMENT(dname, dnumber, mgrssn, mgrstartdate) VALUES (p_DepartmentName, p_DepartmentNumber, p_DepartmentManager, p_ManagerStartDate); COMMIT; END AddDepartment; /

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 48 of 36 Execution of a Stored Functions EXEC AddDepartment ('Info Center', 43, ' ', '28- JUN-2005');

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 49 of 36 Syntax of a Stored Functions CREATE OR REPLACE FUNCTION function_name (parameters IN datatypes) RETURN datatype IS|AS Declaration Section BEGIN Executable Section RETURN variable_name EXCEPTION (optional) Exception Section END;

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 50 of 36 Example of a Stored Functions Given the salary of an employee, calculate the state tax of 2.8% from the salary and return it.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 51 of 36 Example of a Stored Functions CREATE OR REPLACE FUNCTION CalcStateTax ( p_salary IN employee.salary%TYPE) RETURN NUMBER AS BEGIN RETURN (p_salary * 0.028); END CalcStateTax; /

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 52 of 36 Execution of a Stored Functions SELECT fname||' '||lname AS "EMPLOYEE", CalcStateTax(salary) AS "STATE TAX" FROM employee;

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 53 of 36 Execution of a Stored Functions EMPLOYEE STATE TAX James Borg 1540 Jennifer Wallace 1204 Franklin Wong 1120 John Smith 840 Alicia Zelaya 700 Ramesh Narayan 1064 Joyce English 700 Ahmad Jabbar rows selected.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 54 of 36 What is a Trigger Similar to stored procedures and functions. Contains a Declaration, Executable, and Exception sections Differences Triggers are not executed explicitly, they are implicitly execute when a triggering event occurs. (This is called firing the trigger) Triggers do not accept parameters Triggering events are fired by DML Statements ( INSERTs, UPDATEs, or DELETEs) against tables or views AND certain system events

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 55 of 36 Why Use Triggers Complex integrity constraints are not always possible through declarative constraints enabled at table creation time, such as salary may not be lowered. Auditing information, such as who updated an employee's salary, may be required. Remember triggers happen at the basic DML level. Triggers can signal other application that action needs to take place when changes are made to a table. Example, update employee statistics contained in another table.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 56 of 36 Block Structure for a PL/SQL Trigger CREATE [OR REPLACE] TRIGGER trigger_name AFTER | BEFORE | INSTEAD OF a_trigger_event ON table_name (or view_name) [FOR EACH ROW[WHEN trigger_condition]] DECLARE (optional) BEGIN (mandatory) Executes only when trigger_condition is TRUE on a ROW LEVEL TRIGGER EXCEPTION (optional) Exception Section END; (mandatory) NOTE: a_trigger_event may be any combination of an INSERT, DELETE, and/or UPDATE on a table or view

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 57 of 36 Errors and Error Handling Errors can be classified into two types: 1) Compile-Time errors and warnings. After compiling use the command SHOW ERRORS use SET ECHO ON to see statement numbers 2) Run-Time errors occur during execution and throw exception that can be handled by the program.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 58 of 36 Error Handling When errors occur during the execution, control will be branched to the exception handling section. A corresponding error handler will be found to deal with the error.

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 59 of 36 Practice 1 Use the Company database schema, write a stored procedure to add an employee to the employee table, using parameters to input the data. Use your name and following information to test the procedure. FNAME use your first name MINIT use your middle init or a blank space LNAME use your last name SSN make up a 9 digit number BDATE use your birthday (be careful of the date format) STREET make up data CITY Villanova STATE PA ZIP use the Villanova zip code SEX M or F SALARY SUPERSSN DNO 5

Dr. James Dullea, CSC8490 Introduction to PL/SQL Slide 60 of 36 Practice 2 Write a function (called GetDay) that will take in a date as a parameter and return the actual name of the day for that date. Use the function to solve the following problem. Using the data in the employee table from Assignment 1, write an SQL statement or an anonymous block (containing the above function GetDay) that uses your first and last name in a where clause to access the record and returns the actual day of the week that you were born. Hint: GetDay(bdate)