数据库系统概论讲义, 第 8 章编程 SQL,2015,3

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2 数据库系统概论 An Introduction to Database Systems 第八章数据库编程 (ODBC, PL/SQL) 2016, 3, 29

3 Programmatic SQL Three types of programmatic SQL Embedded SQL statements ISO standard specifies embedded support for C, COBOL, Fortran, Pascal, PL/1 Application Programming Interface (API) ODBC JDBC Specific API, like APIs in COBASE Procedure SQL PL/SQL

4 The Open Database Connectivity Standard(1) An alternative approach to embedding SQL statements directly in a host language is to provide programmers with a library of functions that can be invoked from the application software. For many programmers, the use of library routines is standard practice, and they find API a relatively straightforward way to use SQL

5 ODBC Standard(2) The API consists of a set of library function for many of the common types of database access that programmers required, such as connecting to a database, executing SQL, retrieving individual rows of a result table One problem with this approach has been lack of interoperability Programs have to be processed using the DBMS vendor s precompiler and linked with this vendor s API library That will produces DBMS-specific code for each DBMS they want to access

6 ODBC Standard(3) In an attempt to standardize this approach, Microsoft produced the Open Database Connectivity (ODBC) standard ODBC technology provides a common interface for accessing heterogeneous SQL database, based on SQL as the standard for accessing data This interface provides a high degree of interoperatibility: A single application can access different SQL DBMSs through a common set of code

7 ODBC Standard(4) ODBC has emerged as a de facto industry standard. One reason for ODBC popularity is its flexibility Application are not tied to a proprietary vendor API SQL statements can be explicitly included in source code or constructed dynamically at runtime; An application can ignore the underlying data communications protocols; ODBC is designed in conjunction with the X/Open and ISO Call- Level Interface (CLI) standard There are ODBC database drivers available today for many of most popular DBMSs

8 ODBC Architecture(1) The ODBC interface defines the following: A library of function calls that allow an application to connect to a DBMS, execute SQL statement, and retrieve results; A standard way to connect and log on to a DBMS A standard representation of data types A standard set of error codes SQL syntax based on the X/Open and ISO Call-Level Interface (CLI) specification

9 ODBC Architecture(2) The ODBC architecture has four components: Application Driver Manager Driver and Database Agent Data Source

10 ODBC Architecture(3) Application Driver Manager Driver Driver Driver ODBC interface Application Driver Manager Driver Data source Data source Data source Data source Data source Data source Multiple drivers Single drivers

11 ODBC Architecture(4) Q Application Q Q Q Q Q Source T S Source T S Source T S Source T S Source T S

12 ODBC Architecture(4) Q Application ODBC ODBC ODBC ODBC Q Driver Q Driver Q Driver Q Driver Q ODBC Driver Source T S Source T S Source T S Source T S Source T S

13 ODBC Conformance Levels ODBC defines two different conformance levels for drivers: ODBC API ODBC SQL ODBC defines a core grammar that corresponds to the X/Open CAE specification (1992) ISO CLI specification (1995) ODBC 3.0 fully implements both these specifications and adds features commonly needed by developers of screen-based database applications, such as scrollable cursor

14 ODBC SQL Conformance Levels(1) Minimum SQL grammar DDL: CREATE TABLE DROP TABLE DML: Simple SELECT INSERT, UPDATE, DELETE Expressions: simple ( such as A > B+C ) Data Type CHAR, VARCHAR, LONG VARCHAR

15 ODBC SQL Conformance Levels(2) Core SQL grammar Minimum SQL grammar and data types DDL: ALTER TABLE, CREATE INDEX, DROP INDEX, CREATE VIEW, DROP VIEW, GRANT, REVOKE DML: Full SELECT Expressions: subquery, set function Data Type DECIMAL, NUMBER, SMALLINT, INTEGER, REAL, FLOAT, DOUBLE PRECISION

16 ODBC SQL Conformance Levels(3) Extended SQL grammar Minimum and core SQL grammar and data types DML: Outer joins, positioned UPDATE, positioned DELETE, SELECT FOR UPDATE, union Expressions: scalar functions such as SUBSTRING and ABS, date, time Data Type BIT, TINYBIT, BIGING, BINARY, VARBINARY, LONG VARBINARY, DATE, TIME, TIMESTAMP Batch SQL statements Procedure calls

17 Using ODBC(1) Allocate an environment handle: SQLAllocEnv(): allocates memory for the handle and initialize the ODBC Call-Level Interface for use by the application Allocate a connection handle SQLAllocConnect(): A connection consists of a driver and a data source. A connection handle identifies each connection and identifies which driver to use and which data source to use with that driver.

18 Using ODBC (2) Connect to the data source SQLConnect():This call loads a driver and establishes a connection to the named data source. Allocate a statement handle SQLAllocStmt(): A statement handle references statement information such as network information, SQLSTATE values and error messages, cursor name, number of result set columns On completion, all handles must be freed and the connection to the data source terminated

19 Using ODBC (3) Execute SQL statement SQLExecdirect SQLPrepare, SQLExecute

20 Using ODBC (4) Result processing Get information SQLNumResultCols: return the col number SQLDescribeCol, SQLColAttribute: return the coloumn name, data type, ect.. Automatically using cursor for a query SQLBindCol: SQLFetch SQLGetData SQLClosecursor

21 int Getdata_ODBC(Mo_infor_quad *pdata[routenumber],int rmpid) { HENV henv; HDBC hdbc; HSTMT hstmt; RETCODE rc; UCHAR selstmt[500]; UCHAR sname[6] SDWORD snamelen;

22 rc=sqlallocenv(&henv); /* allocate an environment handle */ rc=sqlallocconnect(henv,&hdbc);/* allocate a connection handle */ rc=sqlconnect(hdbc, (unsigned char *)"SQL Server Source", SQL_NTS,/* data source name */ (unsigned char *)"rding", SQL_NTS, /* user identifier */ (unsigned char *) 1234",SQL_NTS); /* password */ /* Note, SQL_NTS directs the driver to determine the length of the string by locating the null-termination character */ if ( rc==sql_success rc == SQL_SUCCESS_WITH_INFO) { rc=sqlallocstmt(sql_handle_stmt,hdbc,&hstmt); /* allocate statement handle */

23 /* Now set up the SELECT statement, execute it, and then bind the columns of the result set */ lstrcp(selstmt, SELECT name from students WHERE SSN = 2345 ); if ( SQLExecDirect(hStmt, selstmt, SQL_NTS)!= SQL_SUCCESS) exit(-1); SQLBindCol(hStmt, 1, SQL_C_CHAR, sname, (SDWORD)sizeof(sName), &snamelen); /* Now fetch the result set, row by row */ while ( rc == SQL_SUCCESS rc == SQL_SUCCESS_WITH_INFO) { rc = SQLFetch(hStmt); if (rc == SQL_SUCCESS rc == SQL_SUCCESS_WITH_INFO) { } } SQLDisconnect(hstmt); } SQLFreeConnect(hdbc); SQLFreeEnv(henv); }

24 PL/SQL PL/SQL is Oracle's Procedural Language extension to SQL. PL/SQL has many programming language features. Program units written in PL/SQL can be stored in compiled form. PL/SQL code is portable across all operating systems that support Oracle. PL/SQL does not support DDL and DCL.

25 PL/SQL Block A PL/SQL block contains logically related SQL and PL/SQL statements. Three sections in a typical PL/SQL block: declaration (optional): declare identifiers (variables and constants). execution (required): execute SQL and PL/SQL statements. exception (optional): perform error handling.

26 Sample Program 1 (1) declare student_name Students.Name%TYPE; student_dept Students.Dept_name%TYPE; begin select Name, Dept_name into student_name, student_dept /* no : needed before host variables */ from Students where SSN = ` ';

27 Sample Program 1 (2) if (student_dept = Computer Science ) then dbms_output.put_line(`this is a CS student.'); else dbms_output.put_line(`this is not a CS student.'); end if; end; / /* end each PL/SQL program with / */

28 Execute PL/SQL Program Save the program in a file: sample1.sql Execute the program in SQL*Plus SQL> start sample1 Enable output to the screen: SQL> set serveroutput on or place set serveroutput on at the beginning of the PL/SQL program.

29 Procedure procedure procedure_name [(parameter, parameter,, parameter)] is [local declarations] begin execution section; [exception section] end; parameter definition: parameter_name [in out in out] data_type

30 Procedure A parameter has a specified name and data type but can also be designated as: IN parameter is used as an input value only OUT parameter is used as an output value only IN OUT parameter is used as both an input and an output value

31 Sample Program (1) set serveroutput on declare v_cid customers.cid%type; v_cname customers.cname%type; v_city customers.city%type; status boolean; procedure get_customer( cust_id in customers.cid%type, cust_name out customers.cname%type, cust_city out customers.city%type, status out boolean) is

32 Sample Program (2) begin select cname, city into cust_name, cust_city from customers where cid = cust_id; status := true; exception when no_data_found then status := false; end; begin v_cid := c001 ; get_customer(v_cid, v_cname, v_city, status);

33 end; / if (status) then Sample Program (3) dbms_output.put_line(v_cid else v_cname v_city); dbms_output.put_line( Customer v_cid not found ); end if;

34 Stored Procedure and Function (1) procedure or function definitions can be stored for later use (in SQL and other PL/SQL blocks). Stored procedures/functions are stored in compiled form. Stored procedures and functions are created by create or replace procedure proc_name create or replace function func_name only in parameter allowed for function.

35 An Example set serveroutput on create or replace procedure get_cus_name( v_cust_id in customers.cid%type) is v_cust_name customers.cname%type; begin select cname into v_cust_name from customers where cid = v_cust_id; dbms_output.put_line( Customer name: v_cust_name); end; / show errors

36 Stored Procedure and Function (2) Compile stored procedure in file proc.sql SQL> start proc show errors displays errors detected during compiling the procedure. Execute stored procedure get_cus_name SQL> execute get_cus_name( c001 );

37 Package A package is a group of related PL/SQL objects (variables, ), procedures, and functions. Each package definition has two parts: package specification package body Package specification provides an interface to the users of the package. Package body contains actual code.

38 Package Specification (1) create or replace package banking as function check_balance (account_no in Accounts.acct_no%type) return Accounts.balance%type; procedure deposit (account_no in Accounts.acct_no%type, amount in Accounts.balance%type);

39 Package Specification (2) procedure withdraw (account_no in Accounts.acct_no%type, amount in Accounts.balance%type); end; / show errors

40 Package Body (1) create or replace package body banking as function check_balance (account_no in Accounts.acct_no%type) return Accounts.balance%type is acct_balance Accounts.balance%type; begin select balance into acct_balance from Accounts where acct_no = account_no; return acct_balance; end;

41 Package Body (2) procedure deposit (account_no in Accounts.acct_no%type, amount in Accounts.balance%type) is begin if (amount <= 0) then dbms_output.put_line( Wrong amount. ); else update Accounts set balance = balance + amount where acct_no = account_no; end if; end;

42 Package Body (3) procedure withdraw (account_no in Accounts.acct_no%type, amount in Accounts.balance%type) is acct_balance Accounts.balance%type;

43 Package Body (4) begin acct_balance := check_balance(account_no); if (amount > acct_balance) then dbms_output.put_line( Insufficient fund. ); else update Accounts set balance = balance - amount where acct_no = account_no; end if; end; end; /* end of the package body */ / show errors

44 Cursor in PL/SQL (1) Consider an SQL query returning multiple rows. How to save the result of the query? Save the result into a big array. No easy way to estimate the size of the result. The result could be too large for any memory-based array. Save one-row-at-a-time: This is the SQL approach.

45 Cursor in PL/SQL (2) Define a cursor: cursor cursor_name is select_statement; Example: cursor c1 is select cid, cname, city from customers; The query defining the cursor is not executed at the declaration time.

46 Working with Cursor (1) open cursor_name; fetch cursor_name into record_or_variable-list; close cursor_name; Open causes the query defining the cursor to be executed.

47 Built-in Package: dbms_sql (1) dbms_sql can be used to dynamically create and execute SQL statements, including DDL statements. Main steps: Open a handle cursor Parse the statement Close the cursor

48 Built-in Package: dbms_sql (2) declare handle integer; stmt varchar2(256); begin stmt := 'create table test (attr1 number(2) ' primary key, attr2 number(4))'; handle := dbms_sql.open_cursor; dbms_sql.parse(handle,stmt,dbms_sql.v7); dbms_output.put_line('table TEST created'); dbms_sql.close_cursor(handle); end; /