Perl DBI for MySQL
This section documents the Perl DBI
interface
for MySQL.
DBI
is a generic interface for many databases. That means that
you can write a script that works with many different database engines
without change. You need a DataBase Driver (DBD) defined for each
database type. For MySQL, this driver is called
DBD::mysql
.
You can get man page information about DBI
with these:
man DBI
man DBI::FAQ
man DBD::mysql
More DBI
/DBD
information
For more information on the Perl5 DBI, please visit the DBI
web
page and read the documentation:
http://www.symbolstone.org/technology/perl/DBI/index.html
For more information on Object Oriented Programming
(OOP) as defined in Perl5, see the Perl OOP page:
http://language.perl.com/info/documentation.html
And of course you can find the latest DBI
information at
the DBI
web page:
http://www.symbolstone.org/technology/perl/DBI/index.html
The DBI interface
Portable DBI methods
connect | Establishes a connection to a database server |
disconnect | Disconnects from the database server |
prepare | Prepares a SQL statement for execution |
execute | Executes prepared statements |
do | Prepares and executes a SQL statement |
quote | Quotes string or BLOB values to be inserted |
fetchrow_array | Fetches the next row as an array of fields. |
fetchrow_arrayref | Fetches next row as a reference array of fields |
fetchrow_hashref | Fetches next row as a reference to a hashtable |
fetchall_arrayref | Fetches all data as an array of arrays |
finish | Finishes a statement and let the system free resources |
rows | Returns the number of rows affected |
data_sources | Returns an array of databases available on localhost |
ChopBlanks | Controls whether fetchrow_* methods trim spaces |
NUM_OF_PARAMS | The number of placeholders in the prepared statement |
NULLABLE | Which columns can be NULL |
trace | Perform tracing for debugging |
MySQL-specific methods
insertid | The latest AUTO_INCREMENT value |
is_blob | Which column are BLOB values |
is_key | Which columns are keys |
is_num | Which columns are numeric |
is_pri_key | Which columns are primary keys |
is_not_null | Which columns CANNOT be NULL . See NULLABLE . |
length | Maximum possible column sizes |
max_length | Maximum column sizes actually present in result |
NAME | Column names |
NUM_OF_FIELDS | Number of fields returned |
table | Table names in returned set |
type | All column types |
The Perl methods are described in more detail in the following sections.
Variables used for method return values have these meanings:
$dbh
Database handle$sth
Statement handle$rc
Return code (often a status)$rv
Return value (often a row count)
Portable DBI methods
connect($data_source, $username, $password)
Use theconnect
method to make a database connection to the data
source. The$data_source
value should begin with
DBI:driver_name:
.
Example uses ofconnect
with theDBD::mysql
driver:$dbh = DBI->connect(“DBI:mysql:$database”, $user, $password);
$dbh = DBI->connect(“DBI:mysql:$database:$hostname”,
$user, $password);
$dbh = DBI->connect(“DBI:mysql:$database:$hostname:$port”,
$user, $password);If the user name and/or password are undefined,
DBI
uses the
values of theDBI_USER
andDBI_PASS
environment variables,
respectively. If you don’t specify a hostname, it defaults to
‘localhost’
. If you don’t specify a port number, it defaults to the
default MySQL port (3306).As of
Msql-Mysql-modules
version 1.2009,
the$data_source
value allows certain modifiers:mysql_read_default_file=file_name
Read `filename’ as an option file.mysql_read_default_group=group_name
The default group when reading an option file is normally the
[client]
group.
By specifying themysql_read_default_group
option, the default group becomes the[group_name]
group.mysql_compression=1
Use compressed communication between the client and server.mysql_socket=/path/to/socket
Specify the pathname of the Unix socket that is used to connect to the server.
Multiple modifiers may be given; each must be preceded by a semicolon.For example, if you want to avoid hardcoding the user name and password into
aDBI
script, you can take them from the user’s `~/.my.cnf’
option file instead by writing yourconnect
call like this:$dbh = DBI->connect(“DBI:mysql:$database”
. “;mysql_read_default_file=$ENV{HOME}/.my.cnf”,
$user, $password);This call will read options defined for the
[client]
group in the
option file. If you wanted to do the same thing, but use options specified
for the[perl]
group as well, you could use this:$dbh = DBI->connect(“DBI:mysql:$database”
. “;mysql_read_default_file=$ENV{HOME}/.my.cnf”
. “;mysql_read_default_group=perl”,
$user, $password);disconnect
Thedisconnect
method disconnects the database
handle from the database.
This is typically called right before you exit from the program.
Example:$rc = $dbh->disconnect;
prepare($statement)
Prepares a SQL statement for execution by the database engine
and returns a statement handle($sth)
which you can use to invoke
theexecute
method.
Typically you handleSELECT
statements
(andSELECT
-like statements
such asSHOW
,DESCRIBE
andEXPLAIN
)
by means of
prepare
andexecute
.
Example:$sth = $dbh->prepare($statement)
or die “Can’t prepare $statement: $dbh->errstr\n”;execute
Theexecute
method executes a prepared statement. For
non-SELECT
statements,execute
returns
the number of rows
affected. I
f no rows are affected,execute
returns“0E0”
,
which Perl treats as zero but regards as true.
ForSELECT
statements,
execute
only starts the SQL query in the database;
you need to use one
of thefetch_*
methods described below to retrieve the data.
Example:$rv = $sth->execute
or die “can’t execute the query: $sth->errstr;do($statement)
Thedo
method prepares and executes a SQL statement and returns the
number of rows affected. If no rows are affected,do
returns
“0E0”
, which Perl treats as zero but regards as true.
This method is
generally used for non-SELECT
statements which cannot be prepared in
advance (due to driver limitations) or which do not need to executed more
than once (inserts, deletes, etc.). Example:$rv = $dbh->do($statement)
or die “Can’t execute $statement: $dbh- >errstr\n”;quote($string)
Thequote
method is used to “escape”
any special characters contained in
the string and to add the required outer quotation marks.
Example:$sql = $dbh->quote($string)
fetchrow_array
This method fetches the next row of data and returns it as an array of
field values. Example:while(@row = $sth->fetchrow_array) {
print qw($row[0]\t$row[1]\t$row[2]\n);
}fetchrow_arrayref
This method fetches the next row of data and returns it as a reference
to an array of field values. Example:while($row_ref = $sth->fetchrow_arrayref) {
print qw($row_ref->[0]\t$row_ref->[1]\t$row_ref->[2]\n);
}fetchrow_hashref
This method fetches a row of data and returns a reference to a hash
table containing field name/value pairs. This method is not nearly as
efficient as using array references as demonstrated above. Example:while($hash_ref = $sth->fetchrow_hashref) {
print qw($hash_ref->{firstname}\t$hash_ref->{lastname}\t\
$hash_ref- > title}\n);
}fetchall_arrayref
This method is used to get all the data (rows) to be returned from the
SQL statement. It returns a reference to an array of references to arrays
for each row. You access or print the data by using a nested
loop. Example:my $table = $sth->fetchall_arrayref
or die “$sth->errstr\n”;
my($i, $j);
for $i ( 0 .. $#{$table} ) {
for $j ( 0 .. $#{$table->[$i]} ) {
print “$table->[$i][$j]\t”;
}
print “\n”;
}finish
Indicates that no more data will be fetched from this statement
handle. You call this method to free up the statement handle and any
system resources associated with it. Example:$rc = $sth->finish;
rows
Returns the number of rows changed (updated, deleted, etc.) by the last
command. This is usually used after a non-SELECT
execute
statement. Example:$rv = $sth->rows;
DT>
NULLABLE
Returns a reference to an array of boolean values; for each element of
the array, a value of TRUE indicates that this
column may containNULL
values.
Example:$null_possible = $sth->{NULLABLE};
NUM_OF_FIELDS
This attribute indicates
the number of fields returned by aSELECT
orSHOW FIELDS
statement. You may use this for checking whether a statement returned a
result: A zero value indicates a non-SELECT
statement like
INSERT
,DELETE
orUPDATE
.
Example:$nr_of_fields = $sth->{NUM_OF_FIELDS};
data_sources($driver_name)
This method returns an array containing names of databases available to the
MySQL server on the host‘localhost’
.
Example:@dbs = DBI->data_sources(“mysql”);
ChopBlanks
This attribute determines whether thefetchrow_*
methods will chop
leading and trailing blanks from the returned values.
Example:$sth->{‘ChopBlanks’} =1;
trace($trace_level)
trace($trace_level, $trace_filename)
Thetrace
method enables or disables tracing. When invoked as a
DBI
class method, it affects tracing for all handles.
When invoked as
a database or statement handle method, it affects tracing for the given
handle (and any future children of the handle).
Setting$trace_level
to 2 provides detailed trace information.
Setting$trace_level
to 0
disables tracing. Trace output goes to the standard error output by
default. If$trace_filename
is specified, the file is opened in
append mode and output for all traced handles is written to that
file. Example:DBI->trace(2); # trace everything
DBI->trace(2,”/tmp/dbi.out”); # trace everything to /tmp/dbi.out
$dth->trace(2); # trace this database handle
$sth->trace(2); # trace this statement handleYou can also enable
DBI
tracing by setting theDBI_TRACE
environment variable. Setting it to a numeric value is equivalent to calling
DBI->(value)
.
Setting it to a pathname is equivalent to calling
DBI->(2,value)
.
MySQL-specific methods
The methods shown below are MySQL-specific and not part of the
DBI
standard. Several of them are now deprecated:
is_blob
, is_key
, is_num
,
is_pri_key
,
is_not_null
, length
,
max_length
, and table
.
Where DBI
-standard alternatives exist, they are noted below.
insertid
If you use theAUTO_INCREMENT
feature of MySQL,
the new
auto-incremented values will be stored here.
Example:$new_id = $sth->{insertid};
As an alternative, you can use
$dbh->{‘mysql_insertid’}
.
is_blob
Returns a reference to an array of boolean values; for each element of the
array, a value of TRUE indicates that the
respective column is aBLOB
.
Example:$keys = $sth->{is_blob};
is_key
Returns a reference to an array of boolean values; for each element of the
array, a value of TRUE indicates that the
respective column is a key.
Example:$keys = $sth->{is_key};
is_num
Returns a reference to an array of boolean values; for each element of the
array, a value of TRUE indicates that the
respective column contains numeric values.
Example:$nums = $sth->{is_num};
is_pri_key
Returns a reference to an array of boolean values; for each element of the
array, a value of TRUE indicates that the respective column is a primary key.
Example:$pri_keys = $sth->{is_pri_key};
is_not_null
Returns a reference to an array of boolean values; for each element of the
array, a value of FALSE indicates that this column may containNULL
values.
Example:$not_nulls = $sth->{is_not_null};
is_not_null
is deprecated; it is preferable to use the
NULLABLE
attribute (described above), since that is a DBI standard.
length
max_length
Each of these methods returns a reference to an array of column sizes. The
length
array indicates the maximum possible sizes that each column may
be (as declared in the table description). Themax_length
array
indicates the maximum sizes actually present in the result table. Example:$lengths = $sth->{length};
$max_lengths = $sth->{max_length};NAME
Returns a reference to an array of column names.
Example:$names = $sth->{NAME};
table
Returns a reference to an array of table names.
Example:
$tables = $sth->{table};
type
Returns a reference to an array of column types.
Example:
$types = $sth->{type};
This tutorial shows how to use Perl to retrieve rows from a MySQL table using Perl DBI.
You require these:
Perl DBD::MySQL module
MySQL server
If you haven’t got DBD::MySQL installed, you can install it with this:
sudo perl -MCPAN -e “install DBD::MySQL”
Then, test if DBD::MySQL is correctly installed with this:
perl -MDBD::MySQL -e “print 1234”
If it prints 1234, you know it is installed.
Create table “domains”
Create this table by running this SQL command in MySQL:
CREATE TABLE IF NOT EXISTS `domains` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(100) NOT NULL,
`url` varchar(100) NOT NULL,
`descr` varchar(100) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=51 ;
Let’s populate this table by executing this INSERT command in MySQL. This will insert 50 rows of domain names, URLs and descriptions.
INSERT INTO `domains` (`id`, `name`, `url`, `descr`) VALUES (1, ’99designs’, ‘www.99designs.com/’, ‘Graphic Design’), (2, ‘AddictLab’, ‘www.addictlab.com/index.php/Home’, ‘Advertising, General’), (3, ‘Article One Partners’, ‘www.articleonepartners.com/’, ‘U.S. Patent Reform / Prior Art Research’), (4, ‘ArtistShare’, ‘www.artistshare.com/home/default.aspx’, ‘Music’), (5, ‘Battle Of Concepts’, ‘battleofconcepts.nl/’, ‘Advertising Creative’), (6, ‘Blellow’, ‘www.blellow.com/’, ‘General’), (7, ‘Bon Bon Kakku’, ‘bonbonkakku.com/’, ‘Graphic Design’), (8, ‘BootB’, ‘www.bootb.com/en/’, ‘Advertising, Creative industries’), (9, ‘Brewtopia’, ‘brewtopia.com.au/about-brewtopia.php’, ‘Brewery’), (10, ‘Brownbook’, ‘www.brownbook.net/’, ‘Business, General’), (11, ‘Cafe Press’, ‘www.cafepress.com/’, ‘Accessories, Clothes, Shopping’), (12, ‘ambrian House’, ‘www.cambrianhouse.com/’, ‘General’), (13, ‘Cameesa’, ‘cameesa.com/’, ‘Apparel / Design’), (14, ‘Catwalk Genius’, ‘www.catwalkgenius.com/default.asp’, ‘Fashion / Design / Shopping’), (15, ‘College Prowler’, ‘collegeprowler.com/’, ‘Education’), (16, ‘Colspark’, ‘www.colspark.com/’, ‘Business / Sales / Marketing’), (17, ‘ConsultingCrowd’, ‘consultingcrowd.com/’, ‘Business, general’), (18, ‘Covestor’, ‘www.covestor.com/’, ‘Investing’), (19, ‘Creatad’, ‘www.creatad.com/en-US/watch.aspx’, ‘Advertising’), (20, ‘Create My Tattoo’, ‘www.createmytattoo.com/altD’, ‘Fashion, Design’), (21, ‘Crowdsound’, ‘www.crowdsound.com/’, ‘Customer feedback’), (22, ‘Crowdspirit’, ‘www.crowdspirit.com/’, ‘General’), (23, ‘Crowdspring’, ‘www.crowdspring.com/’, ‘Design’), (24, ‘CureTogether’, ‘www.curetogether.com/’, ‘Medicine’), (25, ‘Current’, ‘current.com/’, ‘Film/TV’), (26, ‘Data Discoverers’, ‘www.datadiscoverers.com/’, ‘Data’), (27, ‘DoNanza’, ‘www.donanza.com/’, ‘Agrregates All crowdsourcing projects from across the web into one place.’), (28, ‘Dream Heels’, ‘www.dreamheels.com/’, ‘Printed High Heels / Graphic Design / Shopping / Footwear’), (29, ‘Ebbsfleet FC’, ‘www.myfootballclub.co.uk/’, ‘Sports’), (30, ‘Ekotekoo’, ‘projets.ekotekoo.fr/’, ‘Cleantech’), (31, ‘Elastic Lab’, ‘www.elasticlab.com/’, ‘Advertising, Video Production’), (32, ‘Exuve’, ‘www.exuve.com/’, ‘Apparel’), (33, ‘EyeKa’, ‘en.eyeka.com/corporate/offers’, ‘Marketing’), (34, ‘Fat Muffin’, ‘fatmuffin.com/’, ‘Advertising’), (35, ‘FeVote’, ‘www.fevote.com/’, ‘General’), (36, ‘Featurelist’, ‘featurelist.org/’, ‘IT/Computers/Internet’), (37, ‘Feedback2.0’, ‘www.feedback20.com/’, ‘Ideas+Answers’), (38, ‘Fellowforce’, ‘www.fellowforce.com/’, ‘General’), (39, ‘Fiskateers’, ‘www.fiskateers.com/’, ‘Arts/Crafts’), (40, ‘Foldit’, ‘fold.it/portal/’, ‘Science’), (41, ‘Freerisk’, ‘freerisk.org/’, ‘Finance’), (42, ‘Galaxy Zoo’, ‘https://www.galaxyzoo.org/’, ‘Aerospace’), (43, ‘GeniusRocket’, ‘www.geniusrocket.com/’, ‘Video, Design, and Copywriting’), (44, ‘Get Satisfaction’, ‘getsatisfaction.com/’, ‘Customer Service’), (45, ‘Global Lives’, ‘globallives.org/’, ‘Film/TV’), (46, ‘Goosegrade’, ‘www.goosegrade.com/’, ‘Editing’), (47, ‘Graniph’, ‘www.graniph.com/’, ‘Apparel’), (48, ‘Guardian (Tech News on Sun Oracle)’, ‘spreadsheets.google.com/ccc?key=pzqNmTm9PsGwLdHQvGrCPLw’, ‘News’), (49, ‘Halfbakery’, ‘www.halfbakery.com/’, ‘Ideas?’), (50, ‘Zazzle’, ‘www.zazzle.com/’, ‘Accessories, Clothes, General, Shopping’);
Save this script as mysqlselect.pl and run it:
#!/usr/bin/perl -w
use strict;
use DBI;
# Variables
my $str = shift || die “– Please enter a search key for domain name\n”; # search string
my $username = ‘xxxx’; # set your MySQL username
my $password = ‘****’; # set your MySQL password
my $database = ‘dddd’; # set your MySQL database name
my $server = ‘localhost’; # set your server hostname (probably localhost)
# Remove end-of-line from input
chomp $str;
# Get the rows from database
my $dbh = DBI->connect(“DBI:mysql:$database;host=$server”, $username, $password)
|| die “Could not connect to database: $DBI::errstr”;
my $sth = $dbh->prepare(‘select name, url from domains where name like ?’)
|| die “$DBI::errstr”;
$sth->bind_param(1, “%$str%”);
$sth->execute();
# Print number of rows found
if ($sth->rows < 0) {
print "Sorry, no domains found.\n";
} else {
printf ">> Found %d domains\n”, $sth->rows;
# Loop if results found
while (my $results = $sth->fetchrow_hashref) {
my $domainname = $results->{name}; # get the domain name field
my $url = $results->{url}; # get the URL field
printf ” +— \e[1;42m %s (%s)\e[0m\n”, $domainname, $url;
}
}
# Disconnect
$sth->finish;
$dbh->disconnect;