1. M.P. Johnson, DBMS, Stern/NYU, Sp20041 C20.0046: Database Management Systems Lecture #18 Matthew P. Johnson Stern School of Business, NYU Spring, 2004

2. M.P. Johnson, DBMS, Stern/NYU, Sp2004 2 Agenda Previously: Pro*C Next: Project part 3 is due next week More programming for SQL  Embedded SQL Pro*C, SQLJ  PSMs  CLI SQL/CLI in C JDBC in Java DBI/DBDs in Perl PHP (HTML?)

3. M.P. Johnson, DBMS, Stern/NYU, Sp2004 3 Recap: Embedded SQL Host language + Embedded SQL Preprocessor Host Language + function calls Host language compiler Executable Preprocessor Host language compiler Oracle’s Pro*C gcc prog.pc prog.c a.out

4. M.P. Johnson, DBMS, Stern/NYU, Sp2004 4 Limitation of embedded SQL Okay for apps with a fixed set of queries/updates  Maybe very simple kiosks But consider, say, sqlplus or the sqlzoo website  Processes arbitrary queries from user Can we do this with embedded SQL?

5. M.P. Johnson, DBMS, Stern/NYU, Sp2004 5 Dynamic SQL In dynamic SQL, query string can be taken as a parameter, passed to DB Two steps:  Prepare: compiles/optimizes the string  Execute: executes the query Combine together: EXECUTE IMMEDIATE  But separate if query is executed many times (why?) Something like the sqlplus program could be written as a simple dynamic SQL  future homework idea?

6. M.P. Johnson, DBMS, Stern/NYU, Sp2004 6 Dynamic SQL myquery = a SQL variable  not prefixed by : void someQuery() { EXEC SQL BEGIN DECLARE SECTION; char *command; EXEC SQL END DECLARE SECTION; /* command set to some query string */ EXEC SQL PREPARE myquery FROM :command; EXEC SQL EXECUTE myquery; /* or just: */ EXEC SQL EXECUTE IMMEDIATE myquery; } void someQuery() { EXEC SQL BEGIN DECLARE SECTION; char *command; EXEC SQL END DECLARE SECTION; /* command set to some query string */ EXEC SQL PREPARE myquery FROM :command; EXEC SQL EXECUTE myquery; /* or just: */ EXEC SQL EXECUTE IMMEDIATE myquery; }

7. M.P. Johnson, DBMS, Stern/NYU, Sp2004 7 Dynamic SQL example Example script: sample8.pc  See Pro*C tutorialPro*C tutorial Goal: find employees from department 10  Start with query as string sales% proc sample8.pc sales% gcc -I/oracle/precomp/public /oracle/lib/libclntsh.so –osample8 sample8.c sales% sample8 sales% proc sample8.pc sales% gcc -I/oracle/precomp/public /oracle/lib/libclntsh.so –osample8 sample8.c sales% sample8

8. M.P. Johnson, DBMS, Stern/NYU, Sp2004 8 Sketch of sqlplus/mysql EXEC SQL BEGIN DECLARE SECTION; char query[MAX QUERY LENGTH]; EXEC SQL END DECLARE SECTION; /* issue SQL> prompt */ /* read user's text into array query */ EXEC SQL EXECUTE IMMEDIATE :query; /* go back to reissue prompt */ EXEC SQL BEGIN DECLARE SECTION; char query[MAX QUERY LENGTH]; EXEC SQL END DECLARE SECTION; /* issue SQL> prompt */ /* read user's text into array query */ EXEC SQL EXECUTE IMMEDIATE :query; /* go back to reissue prompt */

9. M.P. Johnson, DBMS, Stern/NYU, Sp2004 9 Dynamic SQL example 2 Example script: sample10.pc  See Pro*C tutorialPro*C tutorial Goal: recreate sqlplus/mysql Copy-able commands: http://pages.stern.nyu.edu/~mjohnson/dbms/eg/lec18/proc.txt sales% proc sample10.pc sales% gcc -I/oracle/precomp/public /oracle/lib/libclntsh.so –osample10 sample10.c sales% sample10 sales% proc sample10.pc sales% gcc -I/oracle/precomp/public /oracle/lib/libclntsh.so –osample10 sample10.c sales% sample10

10. M.P. Johnson, DBMS, Stern/NYU, Sp2004 10 Next topic: SQL/CLI Pro*C converts EXEC SQL code  --into what? If we know the API (“Call-Level Interface”), can call library routines by hand Is this better or worse?  Pros & cons Won’t cover in depth

11. M.P. Johnson, DBMS, Stern/NYU, Sp2004 11 CLI: Java Host language + Embedded SQL Preprocessor Host Language + function calls Host language compiler Executable Preprocessor Host language compiler Oracle’s Pro*C javac + jar prog.pc Prog.java Proj.class

12. M.P. Johnson, DBMS, Stern/NYU, Sp2004 12 CLI - Overview Similar to what really happens in embedded SQL implementations. Major approaches:  SQL/CLI - standard of ODBC  JDBC (Java database connectivity)  See http://cbbrowne.com/info/middleware.html for many optionshttp://cbbrowne.com/info/middleware.html Advantages over embedded SQL:  Avoid preprocessor-stage, easier to debug  In th., use same program with several DBMS Disadvantages:  Must keep up to date with API changes  DBMS may have conflicting APIs

13. M.P. Johnson, DBMS, Stern/NYU, Sp2004 13 Next topic: JDBC (Java’s CLI) As expected: Java too can talk to SQL In some ways: much nicer JDBC is an interface  Changes very little  Each vendor writes own plug-in Dev. Strategy: write to API, compile with jar  See http://servlet.java.sun.com/products/jdbc/drivers for 202 (!) JDBC drivershttp://servlet.java.sun.com/products/jdbc/drivers

14. M.P. Johnson, DBMS, Stern/NYU, Sp2004 14 JDBC 1. Load JDBC driver for DBMS: 2. Obtain a connection: Class.forName("oracle.jdbc.driver.OracleDriver") Connection con = DriverManager.getConnection( “jdbc:oracle:thin:@l5.nyu.edu:1521:STN1", username, passwd); Connection con = DriverManager.getConnection( “jdbc:oracle:thin:@l5.nyu.edu:1521:STN1", username, passwd);

15. M.P. Johnson, DBMS, Stern/NYU, Sp2004 15 JDBC 3. Obtain a statement object: 4. Run a query: Or an update: Statement stmt = con.createStatement(); stmt.executeQuery(“SELECT * FROM table”); stmt.executeUpdate(“INSERT INTO tables” + “VALUES(‘abc’, ‘def’)”); stmt.executeUpdate(“INSERT INTO tables” + “VALUES(‘abc’, ‘def’)”);

16. M.P. Johnson, DBMS, Stern/NYU, Sp2004 16 Prepared Statements in JDBC JDBC also supports prepared statements 3. Obtain a PreparedStatement object: 4. Now execute: PreparedStatement ps = con.createStatement( “SELECT * FROM table”); PreparedStatement ps = con.createStatement( “SELECT * FROM table”); ps.executeQuery();

17. M.P. Johnson, DBMS, Stern/NYU, Sp2004 17 Obtaining query results “Cursor” not used, but same idea executeQuery() return a ResultSet: rs.next() advances to new row, returns false if EOF  getInt(i) returns ith column (if an int!) from current row ResultSet rs = ps.executeQuery(); while (rs.next()) { String val1 = rs.getString(1); int val2 = rs.getInt(2); … } while (rs.next()) { String val1 = rs.getString(1); int val2 = rs.getInt(2); … }

18. M.P. Johnson, DBMS, Stern/NYU, Sp2004 18 Java/JDBC/Oracle example Example program: SQLRunner.java  Goal: run the SQL query passed Copy-able commands: http://pages.stern.nyu.edu/~mjohnson/dbms/eg/lec1 8/jdbc.txt sales% cp ~mjohnson/public_html/dbms/eg/lec17/*.java sales% javac SQLRunner.java sales% java SQLRunner "select table_name from user_tables" sales% cp ~mjohnson/public_html/dbms/eg/lec17/*.java sales% javac SQLRunner.java sales% java SQLRunner "select table_name from user_tables"

19. M.P. Johnson, DBMS, Stern/NYU, Sp2004 19 Java/JDBC/MySQL example Example program: MySQLRunner.java  Goal: run the SQL query passed (Nearly) the same as before!  just using different DB/tables/login  mysql.jar is the MySQL J/Connector jar sales% cp ~mjohnson/public_html/dbms/eg/lec17/*.jar sales% javac MySQLRunner.java sales% java -cp.:mysql.jar MySQLRunner "select * from mytab" sales% cp ~mjohnson/public_html/dbms/eg/lec17/*.jar sales% javac MySQLRunner.java sales% java -cp.:mysql.jar MySQLRunner "select * from mytab"