PostgreSQL – Perl


PostgreSQL – Perl Interface

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Installation

The PostgreSQL can be integrated with Perl using Perl DBI module, which is a database access module for the Perl programming language. It defines a set of methods, variables and conventions that provide a standard database interface.

Here are simple steps to install DBI module on your Linux/Unix machine −

$ 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

If you need to install SQLite driver for DBI, then it can be installed as follows −

$ 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

Before you start using Perl PostgreSQL interface, find the pg_hba.conf file in your PostgreSQL installation directory and add the following line −

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

You can start/restart the postgres server, in case it is not running, using the following command −

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

DBI Interface APIs

Following are the important DBI routines, which can suffice your requirement to work with SQLite database from your Perl program. If you are looking for a more sophisticated application, then you can look into Perl DBI official documentation.

S. No. API & Description
1

DBI→connect($data_source, “userid”, “password”, %attr)

Establishes a database connection, or session, to the requested $data_source. Returns a database handle object if the connection succeeds.

Datasource has the form like : DBI:Pg:dbname=$database;host=127.0.0.1;port=5432 Pg is PostgreSQL driver name and testdb is the name of database.
2

$dbh→do($sql)

This routine prepares and executes a single SQL statement. Returns the number of rows affected or undef on error. A return value of -1 means the number of rows is not known, not applicable, or not available. Here $dbh is a handle returned by DBI→connect() call.
3

$dbh→prepare($sql)

This routine prepares a statement for later execution by the database engine and returns a reference to a statement handle object.
4

$sth→execute()

This routine performs whatever processing is necessary to execute the prepared statement. An undef is returned if an error occurs. A successful execute always returns true regardless of the number of rows affected. Here $sth is a statement handle returned by $dbh→prepare($sql) call.
5

$sth→fetchrow_array()

This routine fetches the next row of data and returns it as a list containing the field values. Null fields are returned as undef values in the list.
6

$DBI::err

This is equivalent to $h→err, where $h is any of the handle types like $dbh, $sth, or $drh. This returns native database engine error code from the last driver method called.
7

$DBI::errstr

This is equivalent to $h→errstr, where $h is any of the handle types like $dbh, $sth, or $drh. This returns the native database engine error message from the last DBI method called.
8

$dbh->disconnect()

This routine closes a database connection previously opened by a call to DBI→connect().

Connecting to Database

The following Perl code shows how to connect to an existing database. If the database does not exist, then it will be created and finally a database object will be returned.

#!/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 successfullyn";

Now, let us run the above given program to open our database testdb; if the database is successfully opened then it will give the following message −

Open database successfully

Create a Table

The following Perl program will be used to create a table in previously created database −

#!/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 successfullyn";

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 successfullyn";
}
$dbh->disconnect();

When the above given program is executed, it will create COMPANY table in your testdb and it will display the following messages −

Opened database successfully
Table created successfully

INSERT Operation

The following Perl program shows how we can create records in our COMPANY table created in above example −

#!/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 successfullyn";

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 successfullyn";
$dbh->disconnect();

When the above given program is executed, it will create given records in COMPANY table and will display the following two lines −

Opened database successfully
Records created successfully

SELECT Operation

The following Perl program shows how we can fetch and display records from our COMPANY table created in above example −

#!/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 successfullyn";

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] ."nn";
}
print "Operation done successfullyn";
$dbh->disconnect();

When the above given program is executed, it will produce the following result −

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

The following Perl code shows how we can use the UPDATE statement to update any record and then fetch and display updated records from our COMPANY table −

#!/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 successfullyn";

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 : $rvn";
}
$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] ."nn";
}
print "Operation done successfullyn";
$dbh->disconnect();

When the above given program is executed, it will produce the following result −

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

The following Perl code shows how we can use the DELETE statement to delete any record and then fetch and display the remaining records from our COMPANY table −

#!/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 successfullyn";

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 : $rvn";
}
$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] ."nn";
}
print "Operation done successfullyn";
$dbh->disconnect();

When the above given program is executed, it will produce the following result −

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



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