M.P. Johnson, DBMS, Stern/NYU, Spring C : Database Management Systems Lecture #14 M.P. Johnson Stern School of Business, NYU Spring, 2008

M.P. Johnson, DBMS, Stern/NYU, Spring Agenda Today:  midterms, etc  Proj2, Mysql accounts  SQL programming

M.P. Johnson, DBMS, Stern/NYU, Spring Midterm, etc. Stats:  Possible:  Max:  Mean:  Median:  Stdev:  “Pretty good”: >= Go through MT…

M.P. Johnson, DBMS, Stern/NYU, Spring proj2 Give relational model (normalized as needed) for your project Give interesting queries Create tables (indices, etc.) for it in your account Should be straightforward  If you have an account… Due: 4/2

M.P. Johnson, DBMS, Stern/NYU, Spring NYU Infrastructure Server: sales (sales.stern.nyu.edu) To connect, ssh to sales  e+Search e+Search  I use: WinSCP/Putty Server: i5.nyu.edu (ssh)  User/pass: netid / netid (or nyu pass?) MySQL user/pass: NetID / NetID MySQL shell: mysql  MySQL host: mysql2  See proj3 page for exact command syntax sales% mysql -h mysql2 -u my-NetID -p my-UID  Check that your account works tonight!  phpMyAdmin:

M.P. Johnson, DBMS, Stern/NYU, Spring Programming for SQL Today: from procedural languages to SQL  Pro*C  JDBC Next: DB-backed apps on the web  PHP Later:  PL/SQL, Triggers

M.P. Johnson, DBMS, Stern/NYU, Spring R.A./SQL has limitations Can easily find Alice’s direct subordinates: But: find all of King’s underlings Cannot compute “transitive closure” Cannot express in R.A./SQL! SQL is not “Turing-Complete” NameJobBoss KingPresidentNULL JonesManagerKing BlakeManagerKing FordAnalystJones ScottAnalystJones

M.P. Johnson, DBMS, Stern/NYU, Spring New topic: SQL Programming Can write SQL queries in a SQL interpreter  Command prompt  SQL*Plus (sqlplus) in Oracle  mysql in MySQL Good for experimenting, not for anything non-trivial Better: use a standard programming language  Host language talks to SQL/DB

M.P. Johnson, DBMS, Stern/NYU, Spring Using two languages Q: Why not use just one language? “[W]e can quickly dispense with the idea…” (Ullman, p351) Q: Why not do everything in SQL? A: Not designed as a general-purpose language  No recursion (no factorial!), not Turing-complete  No, e.g., Swing library Q: Why not do everything in the host lang.? A: What Oracle provides is highly non-trivial  Query interpretation, optimizing  Queries stay constant across host languages  Many points of entry Germ of OO: modularize

M.P. Johnson, DBMS, Stern/NYU, Spring Impedance mismatch problem Big problem, though: impedance mismatch  Data structures in our app-programming lang. don’t automatically map onto those in SQL Different types/representations for data In SQL: tables with scalar fields In C: scalars, records (containing records…), pointers, arrays In Java: scalars, objects, references, arrays In Perl: scalars, lists/arrays, hashes/assoc.

M.P. Johnson, DBMS, Stern/NYU, Spring SQL/host interface in embedded SQL So Q: how to transfer data between? A: Shared variables  Some vars in the program can be used by SQL  Prefix var with a :  After query, look here for received data SQL commands embedded in app. code  Identified by EXEC SQL Source code is preprocessed before regular compilation  Result is (e.g.) a C program with library calls

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

M.P. Johnson, DBMS, Stern/NYU, Spring Interface: SQL / Host Language Values get passed through shared variables.  Colons precede shared variables in SQL statements  EXEC SQL demarcates every SQL statement The variable SQLSTATE provides error messages and status reports  “00000” ~ success  “02000” ~ tuple not found Used in loops EXEC SQL BEGIN DECLARE SECTION; char productName[30]; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; EXEC SQL BEGIN DECLARE SECTION; char productName[30]; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION;

M.P. Johnson, DBMS, Stern/NYU, Spring Embedded SQL example Context:  Product (pname, price, quantity, maker)  Purchase (buyer, seller, store, pname)  Company (cname, city)  Person(name, phone, city) Goal 1: Insert a new row in Purchase Goal 2: Look up price of product by name

M.P. Johnson, DBMS, Stern/NYU, Spring Embedded SQL example: insert void simpleInsert() { EXEC SQL BEGIN DECLARE SECTION; char pn[20], cn[30]; /* product-name, company-name */ double p, int q; /* price, quantity */ char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; /* get values for name, price and company somehow */ EXEC SQL INSERT INTO Product(pname, price, quantity, maker) VALUES (:pn, :p, :q, :cn); } void simpleInsert() { EXEC SQL BEGIN DECLARE SECTION; char pn[20], cn[30]; /* product-name, company-name */ double p, int q; /* price, quantity */ char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; /* get values for name, price and company somehow */ EXEC SQL INSERT INTO Product(pname, price, quantity, maker) VALUES (:pn, :p, :q, :cn); }

M.P. Johnson, DBMS, Stern/NYU, Spring Embedded SQL example: look-up int getWindowsPrice() { EXEC SQL BEGIN DECLARE SECTION; double p; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; EXEC SQLSELECT price INTO :p FROM Product WHERE Product.name = ‘Windows’; return p; } int getWindowsPrice() { EXEC SQL BEGIN DECLARE SECTION; double p; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; EXEC SQLSELECT price INTO :p FROM Product WHERE Product.name = ‘Windows’; return p; }

M.P. Johnson, DBMS, Stern/NYU, Spring Embedded SQL example: look-up What about search for arbitrary product? Q: Will this work? int getPrice(char *name) { EXEC SQL BEGIN DECLARE SECTION; int p; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; EXEC SQLSELECT price INTO :p FROM Product WHERE Product.name = :name; return p; } int getPrice(char *name) { EXEC SQL BEGIN DECLARE SECTION; int p; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; EXEC SQLSELECT price INTO :p FROM Product WHERE Product.name = :name; return p; }

M.P. Johnson, DBMS, Stern/NYU, Spring Embedded SQL example: look-up int getPrice(char *name) { EXEC SQL BEGIN DECLARE SECTION; char n[20]; int p; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; strcpy(n, name); /* copy name to local var */ EXEC SQLSELECT price INTO :p FROM Product WHERE Product.name = :n; return p; } int getPrice(char *name) { EXEC SQL BEGIN DECLARE SECTION; char n[20]; int p; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; strcpy(n, name); /* copy name to local var */ EXEC SQLSELECT price INTO :p FROM Product WHERE Product.name = :n; return p; }

M.P. Johnson, DBMS, Stern/NYU, Spring Cursors (quickly to 32) For product’s price, looked up single (scalar) value Q: What if we SELECT multiple fields?  E.g., find all info for some product A: Just list destination vars separated by commas Q: What if find multiple rows?  E.g., find all products above a certain price Use a cursor to step through the results  Each result placed in an array Using cursors: 1. Declare the cursor 2. Open the cursor 3. Fetch tuples one by one 4. Close the cursor

M.P. Johnson, DBMS, Stern/NYU, Spring Cursor loop structure Each time around loop, we  Do a FETCH to obtain next row  Examine SQLSTATE to check success  Can say: What is NO_MORE_TUPLES? #define NO_MORE_TUPLES !(strcmp(SQLSTATE,”02000”)) if(NO_MORE_TUPLES) break;

M.P. Johnson, DBMS, Stern/NYU, Spring Multiple-row look-up example void productToXML() { EXEC SQL BEGIN DECLARE SECTION; char pn[20], cn[30]; double p; int q; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; EXEC SQL DECLARE crs CURSOR FOR SELECT pname, price, quantity, maker FROM Product; EXEC SQL OPEN crs;... void productToXML() { EXEC SQL BEGIN DECLARE SECTION; char pn[20], cn[30]; double p; int q; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; EXEC SQL DECLARE crs CURSOR FOR SELECT pname, price, quantity, maker FROM Product; EXEC SQL OPEN crs;...

M.P. Johnson, DBMS, Stern/NYU, Spring Multiple look-up example printf(" \n"); while (1) { EXEC SQL FETCH FROM crs INTO :n, :p, :q,:c; if (NO_MORE_TUPLES) break; printf(“ \n”); printf(“ %s \n”, n); printf(“ %d \n”, p); printf(“ %d \n”, q); printf(“ %s \n”, c); printf(“ \n”); } EXEC SQL CLOSE crs; printf(“ \n”); } printf(" \n"); while (1) { EXEC SQL FETCH FROM crs INTO :n, :p, :q,:c; if (NO_MORE_TUPLES) break; printf(“ \n”); printf(“ %s \n”, n); printf(“ %d \n”, p); printf(“ %d \n”, q); printf(“ %s \n”, c); printf(“ \n”); } EXEC SQL CLOSE crs; printf(“ \n”); }

M.P. Johnson, DBMS, Stern/NYU, Spring More on Cursors Cursors can traverse both stored tables and queries Cursors can modify a relation as well as read it Cursors can be protected against changes to the underlying relations Can determine the order in which the cursor will get tuples by the ORDER BY keyword in the SQL query The cursor can be a scrolling one: can go forward, backward  +n, -n, Abs(n), Abs(-n)

M.P. Johnson, DBMS, Stern/NYU, Spring Cursor on query not table EXEC SQL DECLARE c CURSOR FOR SELECT beer, price FROM Sells WHERE bar = ‘Izzy''s'; EXEC SQL OPEN CURSOR c; while(1) { EXEC SQL FETCH c INTO :theBeer, :thePrice; if (NOT FOUND) break; /* format and print beer and price */ } EXEC SQL CLOSE CURSOR c; EXEC SQL DECLARE c CURSOR FOR SELECT beer, price FROM Sells WHERE bar = ‘Izzy''s'; EXEC SQL OPEN CURSOR c; while(1) { EXEC SQL FETCH c INTO :theBeer, :thePrice; if (NOT FOUND) break; /* format and print beer and price */ } EXEC SQL CLOSE CURSOR c;

M.P. Johnson, DBMS, Stern/NYU, Spring Modifications with cursors As we traverse through result set, can modify the current row  Can also modify with arb. WHERE clauses NB: In regular SQL, usually modify sets of rows (UPDATE WHERE …) With cursors, we update the last row fetched Simple example: in RentStab table, we decide we want  to raise (e.g., by 5%) all our prices  Unless price > 2000, in which case they’re deleted

M.P. Johnson, DBMS, Stern/NYU, Spring Modification by cursor example void raisePrices() { EXEC SQL BEGIN DECLARE SECTION; double p; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; EXEC SQL DECLARE crs CURSOR FOR SELECT price FROM RentStab; EXEC SQL OPEN crs;... void raisePrices() { EXEC SQL BEGIN DECLARE SECTION; double p; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; EXEC SQL DECLARE crs CURSOR FOR SELECT price FROM RentStab; EXEC SQL OPEN crs;...

M.P. Johnson, DBMS, Stern/NYU, Spring Modification by cursor example while (1) { EXEC SQL FETCH FROM crs INTO :p; if (NO_MORE_TUPLES) break; if (p < 2000) EXEC SQL UPDATE RentStab SET price = 1.05*price; WHERE CURRENT OF RentStab; else EXEC SQL DELETE FROM RentStab WHERE CURRENT OF RentStab; } EXEC SQL CLOSE crs; } while (1) { EXEC SQL FETCH FROM crs INTO :p; if (NO_MORE_TUPLES) break; if (p < 2000) EXEC SQL UPDATE RentStab SET price = 1.05*price; WHERE CURRENT OF RentStab; else EXEC SQL DELETE FROM RentStab WHERE CURRENT OF RentStab; } EXEC SQL CLOSE crs; }

M.P. Johnson, DBMS, Stern/NYU, Spring 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?

M.P. Johnson, DBMS, Stern/NYU, Spring 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?)

M.P. Johnson, DBMS, Stern/NYU, Spring Dynamic SQL myquery = a SQL variable  not prefixed by : void runQuery() { 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 :command; } void runQuery() { 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 :command; }

M.P. Johnson, DBMS, Stern/NYU, Spring Sketch of sqlplus Something like the sqlplus program could be written as a simple dynamic SQL  future hw idea? 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 */

M.P. Johnson, DBMS, Stern/NYU, Spring Interface: SQL/Host Language Two languages: SQL, host (C/Java/whatever) Benefits:  DB code (SQL is portable)  SQL, host language focus on own strengths SQL code placed in host language code SQL and host language have diff. data types  “impedance mismatch”  Data transferred with “shared variables” Use cursors to access/modify data Error messages placed in SQLSTATE

M.P. Johnson, DBMS, Stern/NYU, Spring Programs with 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

M.P. Johnson, DBMS, Stern/NYU, Spring Next topic: SQL/CLI (break?) 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

M.P. Johnson, DBMS, Stern/NYU, Spring 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

M.P. Johnson, DBMS, Stern/NYU, Spring CLI - Overview Similar to what really happens in embedded SQL implementations. Major approaches:  SQL/CLI - standard of ODBC  JDBC - Java database connectivity  See 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  “write once, run everywhere” Disadvantages:  Must keep up to date with API changes  DBMS may have conflicting APIs

M.P. Johnson, DBMS, Stern/NYU, Spring 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, run w/ the DBMS jar  See for 219 (!) JDBC drivershttp://servlet.java.sun.com/products/jdbc/drivers

M.P. Johnson, DBMS, Stern/NYU, Spring JDBC 1. Load JDBC driver for DBMS: 2. Obtain a connection: What does this mean? Find info here: $ORACLE_HOME/network/admin/tnsnames.ora Class.forName("oracle.jdbc.driver.OracleDriver") Connection con = DriverManager.getConnection( username, passwd); Connection con = DriverManager.getConnection( username, passwd);

M.P. Johnson, DBMS, Stern/NYU, Spring 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 mytable ” + “VALUES(‘abc’, ‘def’)”); stmt.executeUpdate(“INSERT INTO mytable ” + “VALUES(‘abc’, ‘def’)”);

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

M.P. Johnson, DBMS, Stern/NYU, Spring Obtaining query results “Cursor” not used, but same idea executeQuery() returns a ResultSet: rs.next() advances to new row, returns false if EOF  getInt(i) returns ith column (if an int!) from current row  can look up metadata… 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); … }

M.P. Johnson, DBMS, Stern/NYU, Spring Java & parameter-based SQL Like SQL/CLI in C, Java also supports parameterized queries (why?) 1. Prepare structure of query 2. Then can set values When better? PreparedStatement ps = conn.prepareStatement( "SELECT * FROM table WHERE f1 = ? and f2 = ?"); ps.setString(1, "abc"); ps.setString(2, "def"); ResultSet rs = ps.executeQuery();... PreparedStatement ps = conn.prepareStatement( "SELECT * FROM table WHERE f1 = ? and f2 = ?"); ps.setString(1, "abc"); ps.setString(2, "def"); ResultSet rs = ps.executeQuery();...

M.P. Johnson, DBMS, Stern/NYU, Spring Also: ODBC Used by Microsoft platforms/tools, others Access:  Start | Control Panel | Administrative Tools | Data Sources (ODBC) Similar to JDBC Won’t cover

M.P. Johnson, DBMS, Stern/NYU, Spring Next time DBs on the web: PHP, etc. Start working through PHP/MySQL tutorials on website  Skim relevant parts of ch.7 If you (and your group members) can’t log in, let me know ASAP