1. Embedded SQL John Ortiz

2. Lecture 15Embedded SQL2 Why Isn’t Interactive SQL Enough?  How to do this using interactive SQL?  Print a well-formatted transcript of a student with either a name or an id  What does it take for someone to use SQL? To know schemas, syntax, semantics, mathematics, logic, …  Solution? Write application programs to help naïve users to manipulate the data.  How to access database from within a program?

3. Lecture 15Embedded SQL3 Idea of Embedded SQL  Combine the power of both SQL & a general purpose programming language.  Use (embedded) SQL to perform data retrieval and updates.  Use the general purpose programming language (host PL) to perform more complex data processing and to provide a friendly user interface.

4. Lecture 15Embedded SQL4 Oracle API  Support embedded SQL through five host PLs (pro*languages) C/C++, Cobol, PL/I, Ada, Pascal  Oracle8i supports Java/JDBC and SQLJ  SQL stmts are placed in host PL programs  Data flow from database to program variables and vice versa  Two step compilation:  Precompilation: prog.pc  prog.cc  Compilation: prog.cc  prog.o

5. Lecture 15Embedded SQL5 A Sample Pro*C/C++ Program  The program is sample1.pcsample1.pc  Common tasks:  Declare variables interfacing SQL & host PL  Prepare for any SQL error  Include sqlca (communication area)  Use whenever sqlerror, …  Provide for error processing  Connect to database  Issue SQL statements  Disconnect the database

6. Lecture 15Embedded SQL6 PL & SQL Variables  Every variable used to get data from & pass data to database must be declared in a declare section exec sql begin declare section; varchar user_name[20], passwd[10]; … exec sql end declare section;  Must use SQL data types  Can appear in both SQL (preceded by a colon :user_name) & PL statements (no colon)

7. Lecture 15Embedded SQL7 PL & SQL Variables (cont.)  Oracle Pro*C pre-processor will convert varchar user_name[20]; to: struct { unsigned short len; unsigned char arr[20]; } user_name;  SQL string is not ‘\0’-ended, but C string is  Variables must have comparable types to get data from table columns

8. Lecture 15Embedded SQL8 Handle SQL Errors  SQLCA (p.121): SQL Communication area is a predefined data structure used to pass control information from Oracle to application program  Error code: sqlca.sqlcode=0 successful; > 0 value not found; < 0 error  Can also use predefined error types in whenever: sqlerror, not found, sqlwarning, …  Common error handling actions: goto Label, continue, stop, do func, do break, do return, …

9. Lecture 15Embedded SQL9 Embedded SQL Statements  Every SQL statement is preceded by exec sql  Can use all SQL statements plus special ones.  Connect, disconnect  Whenever  Select … into … from …  Rollback  Commit  Statements declare and use cursors  Statements define and execute dynamic queries

10. Lecture 15Embedded SQL10 Transaction Control Statements  A transaction is modeled by a sequence of database update operations  Operations of a transaction should either all be successfully executed or none is executed  When a failure occurs, all updates done so far need to be undone  Explicit control:  Start: set transaction [read only, read write]  Undo: rollback  End: commit

11. Lecture 15Embedded SQL11 Sample Program Using A Cursor  How does a program handle query result containing more than one tuple?  Use a cursor. See sample2.pcsample2.pc  A cursor is a “window” through which one tuple can be accessed.  A cursor must be declared with a query  Open cursor executes the query  Fetch cursor moves to the next tuple  A cursor can be closed and re-opened

12. Lecture 15Embedded SQL12 Dynamic SQL  Create SQL statements at run time and then execute the newly created statements.  General framework:  Declare a host string variable.  Place an SQL statement in the variable at run-time.  Let the DBMS parse & execute the SQL statement in the host variable.

13. Lecture 15Embedded SQL13 Why Dynamic SQL  Consider relation: Projects(Pno, Name, Budget, Duration)  How to write a program to delete projects that satisfy some yet unknown conditions? delete Projects where  Some possible types of conditions: (1) Budget > 2000000 (2) Budget > 2000000 and Duration > 24 (3)Name = 'Manned Spacecraft to Mars‘  Why isn’t static SQL a viable solution?

14. Lecture 15Embedded SQL14 Methods of Dynamic SQL  Method 1: Non-query statement w/o host var. delete from emp where deptno = 20  Method 2: Non-query w/ known # of input var. delete from emp where empno = :eid  Method 3: Query w/ known select-list & input host variables. select ename from emp where deptno = :dno  Method 4: Query w/ unknown select-list & var. select from emp

15. Lecture 15Embedded SQL15 Execute-Immediate Statement  A sample programsample program  execute immediate causes the dynamic SQL statement to be compiled and executed immediately.  General execute immediate statement: exec sql execute immediate :host_variable;  Implement Method 1.

16. Lecture 15Embedded SQL16 Prepare-Execute Statement  A sample programsample program  prepare stmt_name from :host_variable compiles the SQL query in host_variable and then saves the prepared result in stmt_name.  stmt_name is an SQL identifier and needs not be explicitly declared.  Implement Method 2: The host_variable can contain any SQL statement other than a query and can have a known number of placeholders.  Prepare once, run many times (with different values in input host variables).

17. Lecture 15Embedded SQL17 Pro*C/C++ and PL/SQL  On Oracle, Pro*C/C++ programs may contain any SQL statement and PL/SQL blocks.  See this sample programsample program  Precompiled and stored PL/SQL procedures and functions can be used directly in embedded SQL statement exec sql execute p(…)

18. Lecture 15Embedded SQL18 Oracle JDBC  JDBC (Java Database Connectivity): API that allows Java applications and applets to connect to Oracle databases, send SQL statements, and receive data from databases.  Need to set up CLASSPATH environment variable.  See QueryUnivDB.javaQueryUnivDB.java

19. Lecture 15Embedded SQL19 JDBC: Program Tasks  Import Java SQL API library  Load JDBC driver: Class.forName(…)  Create a DB connection DriveManager.getConnection( )  Create a query statement object  Create a result object by executing the query  Process the result  Close the query  Close the connection

20. Lecture 15Embedded SQL20 Oracle SQLJ  Java with embedded SQL (prec. w/ #sql)  Part of the new SQL 1999 Standard.  Much easier to use:  Connect to database  Create iterators for query results  Oracle8i only supports JDK1.1  Need two compilation steps:  sqlj file[.sqlj]  javac file.java  See QueryUnivDB.sqljQueryUnivDB.sqlj

21. Lecture 15Embedded SQL21 Embedded SQL Summary  Many additional statements handling communication between database and PL system  Special handling of multiple tuple result (cursor)  Must handle errors and exceptions generated by DBMS  Must pay special attention to program structure (goto, whenever not found,… )  JDBC & SQLJ have much better DB-PL interface

22. Lecture 15Embedded SQL22 Look Ahead  Next topic: Storage System  Read textbook:  Chapter 5