数据库系统概论idke.ruc.edu.cn/xfmeng/course/Introduction to Database... · · 2016-03-23Three sections in a typical PL/SQL block: ... (variables and constants). • execution

数据库系统概论讲义，第8章编程SQL，2015，3


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

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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


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


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


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


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


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



• The ODBC architecture has four components: – Application – Driver Manager – Driver and Database Agent – Data Source



Application

Driver Manager

Driver Driver Driver

Data source

Data source

Data source

Data source

Data source

Data source

Application

Driver Manager

Driver

ODBC interface

Multiple drivers Single drivers



Application

Source TS

Source TS

Source TS

Source TS

Source TS

Q

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Application

Source TS

Source TS

Source TS

Source TS

Source TS

Q

Q’ Q’ Q’ Q’ Q’ ODBC Driver

ODBC Driver

ODBC Driver

ODBC Driver

ODBC Driver


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


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


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


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


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.


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


Using ODBC (3)

• Execute SQL statement – SQLExecdirect – SQLPrepare, SQLExecute


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


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;


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 */


/* 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); }


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.


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.


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 = `123456789';


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 / */


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.


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


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


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


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);


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


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.


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


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’);


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.


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);


Package Specification (2)

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


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;


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;


Package Body (3)

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


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


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.


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.


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.


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


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; /

Documents

数据库系统概论idke.ruc.edu.cn/xfmeng/course/Introduction to Database... · · 2016-03-23Three sections in a typical PL/SQL block: ... (variables and constants). • execution