Postgresql 简明教程

PostgreSQL - Perl Interface

Installation

PostgreSQL 可以使用 Perl 中的 Perl DBI 模块进行集成，该模块是 Perl 编程语言的数据库访问模块。其定义了一组方法、变量和约定，以提供标准数据库接口。

以下是在 Linux/Unix 计算机上安装 DBI 模块的简单步骤：

$ wget http://search.cpan.org/CPAN/authors/id/T/TI/TIMB/DBI-1.625.tar.gz
$ tar xvfz DBI-1.625.tar.gz
$ cd DBI-1.625
$ perl Makefile.PL
$ make
$ make install

如果需要为 DBI 安装 SQLite 驱动，那么它可以按如下方式安装 −

$ wget http://search.cpan.org/CPAN/authors/id/T/TU/TURNSTEP/DBD-Pg-2.19.3.tar.gz
$ tar xvfz DBD-Pg-2.19.3.tar.gz
$ cd DBD-Pg-2.19.3
$ perl Makefile.PL
$ make
$ make install

在开始使用 Perl PostgreSQL 接口之前，在 PostgreSQL 安装目录中找到 pg_hba.conf 文件，并添加以下行：

# IPv4 local connections:
host    all         all         127.0.0.1/32          md5

如果 postgres 服务未运行，可以使用以下命令启动/重新启动它：

[root@host]# service postgresql restart
Stopping postgresql service:                               [  OK  ]
Starting postgresql service:                               [  OK  ]

DBI Interface APIs

以下是一些重要的 DBI 例程，它们可以满足您从 Perl 程序处理 SQLite 数据库的需求。如果您正在寻找更精细的应用程序，那么可以查看 Perl DBI 官方文档。

S. No.

API & Description

1

DBI→connect($data_source, "userid", "password", \%attr) 建立与请求的 $data_source 的数据库连接或会话。如果连接成功，则会返回一个数据库处理对象。数据源的格式如下： DBI:Pg:dbname=$database;host=127.0.0.1;port=5432 Pg 是 PostgreSQL 驱动程序名称，testdb 是数据库的名称。

2

$dbh→do($sql) 此例程准备并执行一个 SQL 语句。返回受影响的行数或错误时的 undef。返回值 -1 表示无法得知、不可用或不可获取行数。此处 $dbh 是由 DBI→connect() 调用返回的处理程序。

3

$dbh→prepare($sql) 此例程为数据库引擎准备一个语句以供之后执行，并返回一个语句处理对象引用。

4

$sth→execute() 此例程执行执行已准备语句所需的任何处理。如果出现错误，则返回一个 undef。无论受影响的行数如何，成功执行始终返回 true。此处 $sth 是由 $dbh→prepare($sql) 调用返回的语句处理程序。

5

$sth→fetchrow_array() 此例程获取下一行数据，并以包含字段值的一个列表的形式返回它。null 字段在列表中返回为 undef 值。

6

$DBI::err 这等同于 $h→err，其中 $h 是任何类型处理程序，例如 $dbh、$sth 或 $drh。这将返回从最后调用的驱动程序方法中返回的原生数据库引擎错误代码。

7

$DBI::errstr 这等同于 $h→errstr，其中 $h 是任何类型处理程序，例如 $dbh、$sth 或 $drh。这将返回从最后调用的 DBI 方法返回的原生数据库引擎错误消息。

8

$dbh→disconnect() 此例程关闭先前通过调用 DBI→connect() 打开的数据库连接。

Connecting to Database

以下 Perl 代码显示了如何连接到现有数据库。如果数据库不存在，那么将创建一个数据库，最后将返回一个数据库对象。

#!/usr/bin/perl

use DBI;
use strict;

my $driver  = "Pg";
my $database = "testdb";
my $dsn = "DBI:$driver:dbname = $database;host = 127.0.0.1;port = 5432";
my $userid = "postgres";
my $password = "pass123";
my $dbh = DBI->connect($dsn, $userid, $password, { RaiseError => 1 })
   or die $DBI::errstr;

print "Opened database successfully\n";

现在，让我们运行给定上面的程序来打开我们的数据库 testdb ；如果数据库打开成功，则它将给出以下消息 −

Open database successfully

Create a Table

下面的 Perl 程序将用于在之前创建的数据库中创建一个表 −

#!/usr/bin/perl

use DBI;
use strict;

my $driver   = "Pg";
my $database = "testdb";
my $dsn = "DBI:$driver:dbname=$database;host=127.0.0.1;port=5432";
my $userid = "postgres";
my $password = "pass123";
my $dbh = DBI->connect($dsn, $userid, $password, { RaiseError => 1 })
   or die $DBI::errstr;
print "Opened database successfully\n";

my $stmt = qq(CREATE TABLE COMPANY
      (ID INT PRIMARY KEY     NOT NULL,
      NAME           TEXT    NOT NULL,
      AGE            INT     NOT NULL,
      ADDRESS        CHAR(50),
      SALARY         REAL););
my $rv = $dbh->do($stmt);
if($rv < 0) {
   print $DBI::errstr;
} else {
   print "Table created successfully\n";
}
$dbh->disconnect();

当执行给定上面的程序时，它将在您的 testdb 中创建 COMPANY 表，然后显示以下消息 −

Opened database successfully
Table created successfully

INSERT Operation

下面的 Perl 程序展示了我们如何在上面示例中创建的 COMPANY 表中创建记录 −

#!/usr/bin/perl

use DBI;
use strict;

my $driver   = "Pg";
my $database = "testdb";
my $dsn = "DBI:$driver:dbname = $database;host = 127.0.0.1;port = 5432";
my $userid = "postgres";
my $password = "pass123";
my $dbh = DBI->connect($dsn, $userid, $password, { RaiseError => 1 })
   or die $DBI::errstr;
print "Opened database successfully\n";

my $stmt = qq(INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
   VALUES (1, 'Paul', 32, 'California', 20000.00 ));
my $rv = $dbh->do($stmt) or die $DBI::errstr;

$stmt = qq(INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
   VALUES (2, 'Allen', 25, 'Texas', 15000.00 ));
$rv = $dbh->do($stmt) or die $DBI::errstr;

$stmt = qq(INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
   VALUES (3, 'Teddy', 23, 'Norway', 20000.00 ));
$rv = $dbh->do($stmt) or die $DBI::errstr;

$stmt = qq(INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
   VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 ););
$rv = $dbh->do($stmt) or die $DBI::errstr;

print "Records created successfully\n";
$dbh->disconnect();

当执行给定上面的程序时，它将在 COMPANY 表中创建给定的记录，然后显示以下两行 −

Opened database successfully
Records created successfully

SELECT Operation

下面的 Perl 程序展示了我们如何在上面示例中创建的 COMPANY 表中获取并显示记录 −

#!/usr/bin/perl

use DBI;
use strict;

my $driver   = "Pg";
my $database = "testdb";
my $dsn = "DBI:$driver:dbname = $database;host = 127.0.0.1;port = 5432";
my $userid = "postgres";
my $password = "pass123";
my $dbh = DBI->connect($dsn, $userid, $password, { RaiseError => 1 })
   or die $DBI::errstr;
print "Opened database successfully\n";

my $stmt = qq(SELECT id, name, address, salary  from COMPANY;);
my $sth = $dbh->prepare( $stmt );
my $rv = $sth->execute() or die $DBI::errstr;
if($rv < 0) {
   print $DBI::errstr;
}
while(my @row = $sth->fetchrow_array()) {
      print "ID = ". $row[0] . "\n";
      print "NAME = ". $row[1] ."\n";
      print "ADDRESS = ". $row[2] ."\n";
      print "SALARY =  ". $row[3] ."\n\n";
}
print "Operation done successfully\n";
$dbh->disconnect();

当执行给定上面的程序时，它将产生以下结果 −

Opened database successfully
ID = 1
NAME = Paul
ADDRESS = California
SALARY =  20000

ID = 2
NAME = Allen
ADDRESS = Texas
SALARY =  15000

ID = 3
NAME = Teddy
ADDRESS = Norway
SALARY =  20000

ID = 4
NAME = Mark
ADDRESS = Rich-Mond
SALARY =  65000

Operation done successfully

UPDATE Operation

下面的 Perl 代码展示了我们如何使用 UPDATE 语句更新任何记录，然后从 COMPANY 表中获取并显示已更新的记录 −

#!/usr/bin/perl

use DBI;
use strict;

my $driver   = "Pg";
my $database = "testdb";
my $dsn = "DBI:$driver:dbname = $database;host = 127.0.0.1;port = 5432";
my $userid = "postgres";
my $password = "pass123";
my $dbh = DBI->connect($dsn, $userid, $password, { RaiseError => 1 })
   or die $DBI::errstr;
print "Opened database successfully\n";

my $stmt = qq(UPDATE COMPANY set SALARY = 25000.00 where ID=1;);
my $rv = $dbh->do($stmt) or die $DBI::errstr;
if( $rv < 0 ) {
   print $DBI::errstr;
}else{
   print "Total number of rows updated : $rv\n";
}
$stmt = qq(SELECT id, name, address, salary  from COMPANY;);
my $sth = $dbh->prepare( $stmt );
$rv = $sth->execute() or die $DBI::errstr;
if($rv < 0) {
   print $DBI::errstr;
}
while(my @row = $sth->fetchrow_array()) {
      print "ID = ". $row[0] . "\n";
      print "NAME = ". $row[1] ."\n";
      print "ADDRESS = ". $row[2] ."\n";
      print "SALARY =  ". $row[3] ."\n\n";
}
print "Operation done successfully\n";
$dbh->disconnect();

当执行给定上面的程序时，它将产生以下结果 −

Opened database successfully
Total number of rows updated : 1
ID = 1
NAME = Paul
ADDRESS = California
SALARY =  25000

ID = 2
NAME = Allen
ADDRESS = Texas
SALARY =  15000

ID = 3
NAME = Teddy
ADDRESS = Norway
SALARY =  20000

ID = 4
NAME = Mark
ADDRESS = Rich-Mond
SALARY =  65000

Operation done successfully

DELETE Operation

下面的 Perl 代码展示了我们如何使用 DELETE 语句删除任何记录，然后从 COMPANY 表中获取并显示剩下的记录 −

#!/usr/bin/perl

use DBI;
use strict;

my $driver   = "Pg";
my $database = "testdb";
my $dsn = "DBI:$driver:dbname = $database;host = 127.0.0.1;port = 5432";
my $userid = "postgres";
my $password = "pass123";
my $dbh = DBI->connect($dsn, $userid, $password, { RaiseError => 1 })
   or die $DBI::errstr;
print "Opened database successfully\n";

my $stmt = qq(DELETE from COMPANY where ID=2;);
my $rv = $dbh->do($stmt) or die $DBI::errstr;
if( $rv < 0 ) {
   print $DBI::errstr;
} else{
   print "Total number of rows deleted : $rv\n";
}
$stmt = qq(SELECT id, name, address, salary  from COMPANY;);
my $sth = $dbh->prepare( $stmt );
$rv = $sth->execute() or die $DBI::errstr;
if($rv < 0) {
   print $DBI::errstr;
}
while(my @row = $sth->fetchrow_array()) {
      print "ID = ". $row[0] . "\n";
      print "NAME = ". $row[1] ."\n";
      print "ADDRESS = ". $row[2] ."\n";
      print "SALARY =  ". $row[3] ."\n\n";
}
print "Operation done successfully\n";
$dbh->disconnect();

当执行给定上面的程序时，它将产生以下结果 −

Opened database successfully
Total number of rows deleted : 1
ID = 1
NAME = Paul
ADDRESS = California
SALARY =  25000

ID = 3
NAME = Teddy
ADDRESS = Norway
SALARY =  20000

ID = 4
NAME = Mark
ADDRESS = Rich-Mond
SALARY =  65000

Operation done successfully