Lecture 27 10/30/15. CMPSC431W: Database Management Systems. Instructor: Yu- San Lin

Transcription

1 CMPSC431W: Database Management Systems Lecture 27 10/30/15 Instructor: Yu- San Lin Course Website: hcp:// Slides based on McGraw- Hill & Dr. Wang- Chien Lee 1

2 Review last Sme Two approaches for integrason: Embed SQL, e.g., Embedded SQL API, e.g., JDBC Cursor: mostly needed for SELECT commands Dynamic SQL: commands prepared in runsme JDBC Architecture Drivers 2

3 Four Types of JDBC Drivers App. JDBC ODBC App. JDBC DBAPI App. JDBC JDBC ODBC App. JDBC DBAPI middleware 3

4 JDBC Example: Obtain Metadata DatabaseMetaData dmd = con.getmetadata(); ResultSet tablesrs = dmd.gettables(null, null, null, null); string tablename; while(tablesrs.next()) { tablename = tablesrs.getstring("table_name"); // print out the attributes of this table System.out.println("The attributes of table " + tablename + " are:"); ResultSet columnsrs = dmd.getcolumns(null, null, tablename, null); while(columnsrs.next()){ System.out.print(columnsRS.getString("COLUMN_NAME") + " "); } } // print out the primary keys of this table System.out.println("The keys of table " + tablename + " are:"); ResultSet keysrs = dmd.getprimarykeys(null, null, tablename); while(keysrs.next()){ System.out.print(keysRS.getString("COLUMN_NAME") + " "); } 4

5 SQLJ Complements JDBC with a (semi- ) stasc query model Close to Compiler can perform the following at compilason Sme: syntax checks strong type checks consistency of the query with the schema 5

6 SQLJ (cont.) All arguments always bound to the same variable: #sql = { SELECT name, rating INTO :name, :rating FROM Books WHERE sid = :sid; }; Compare to JDBC: // assume we have a ResultSet cursor rs author = rs.getstring(3); if (author == Feynman ) { ftitle = rs.getstring(2); } else { otitle = rs.getstring(2); } 6

7 Bookstore Example: SQLJ String title; Float price; String author; #sql iterator Books (String title, Float price); Books books; // the application sets the author // execute the query and open the cursor #sql books = { SELECT title, price INTO :title, :price FROM Books WHERE author = :author }; // retrieve results while (books.next()){ System.out.println(books.title() + "," + books.prices()); } books.close() 7

8 Bookstore Example: JDBC PreparedStatement stmt = connection.preparestatement( "SELECT title, price FROM Books WHERE author =?"); // set the parameter in the query and execute it stmt.setstring(1, author); ResultSet rs = stmt.executequery(); // retrieve the results while(rs.next()){ System.out.println(rs.getString(1) + "," + rs.getfloat(2)); } 8

9 Usage of SQLJ Iterator 1. Declare the iterator class 2. InstanSate an iterator object from the new iterator class 3. IniSalize the iterator using a SQL statement 4. IteraSvely, read the rows from the iterator object 5. Close the iterator object 9

10 Types of SQLJ Iterators iterator Needs both variable type and name Allows retrieval of columns by name iterator Needs only variable type Uses FETCH..INTO construct (similar to Embedded SQL) * Both iterator types have the same performance 10

11 Named v.s. PosiSonal Iterator Named iterator #sql iterator Books (String title, Float price); Books books; #sql books = { SELECT title, price INTO :title, :price FROM Books}; while (books.next()){ System.out.println(books.title() + "," + books.prices()); } Posi-onal iterator #sql iterator Books (String, Float); Books books; while (true){ #sql {FETCH :books INTO :title, :price}; } if (books.endfetch()) { } break; 11

12 Stored Procedures Running applicason logic directly at the database has the advantages: Minimize the amount of data transferred between the database server and the client issuing the SQL statement USlizing the full power of the database server What is a stored procedure: Program executed through a single SQL statement Executed in the process space of the server 12

13 Advantages of Stored Procedures Can encapsulate applicason logic while staying close to the data Reuse of applicason logic by different users Avoid tuple- at- a- Sme return of records through cursors 13

14 Stored Procedures: Examples CREATE PROCEDURE ShowNumberOfOrders SELECT C.cid, C.cname, COUNT(*) FROM Customers C, Orders O WHERE C.cid = O.cid GROUP BYC.cid, C.cname 14

15 Stored Procedures: Examples (cont.) Stored procedures can have parameters CREATE PROCEDURE AddInventory ( ) IN book_isbn CHAR(10), IN addedqty INTEGER UPDATE Books SET qty_in_stock = qty_in_stock + addedqty WHERE book_isbn = isbn 15

16 Stored Procedures: Examples (cont.) Stored procedures do not have to be wricen in SQL CREATE PROCEDURE RankCustomers (IN number INTEGER) LANGUAGE Java EXTERNAL NAME file:///c:/storedprocedures/ rank.jar 16

17 Calling Stored Procedures: Embedded SQL EXEC SQL BEGIN DECLARE SECTION char isbn[10]; long qty; EXEC SQL END DECLARE SECTION // set isbn and qty to some values EXEC SQL CALL AddInventory(:isbn, :qty); 17

18 Calling Stored Procedures: JDBC CallableStatement cstmt = con.preparecall( {call ShowNumberOfOrders} ); ResultSet = cstmt.executequery() while (rs.next()) 18

19 Calling Stored Procedures: SQLJ // create the cursor class #sql Iterator CustomerInfo(int cid, String cname, int count); // create the cursor CustomerInfo customerinfo; // call the stored procedure #sql customerinfo = {CALL ShowNumberOfOrders}; while(customerinfo.next()) { System.out.println(customerinfo.cid() +, + customerinfo.count()); } 19

20 Summary allows execution of parameterized static queries within a host language allows execution of completely ad-hoc queries within a host language mechanism allows retrieval of one record at a time and bridges impedance mismatch between host language and SQL 20

21 Summary (cont.) such as JDBC introduce a layer of abstraction between application and DBMS : Static; queries checked at compile-time execute application logic directly at the server 21