DBD::mysql(3pm) User Contributed Perl Documentation DBD::mysql(3pm)NAMEDBD::mysql - MySQL driver for the Perl5 Database Interface (DBI)
SYNOPSIS
use DBI;
my $dsn = "DBI:mysql:database=$database;host=$hostname;port=$port";
my $dbh = DBI->connect($dsn, $user, $password);
my $sth = $dbh->prepare(
'SELECT id, first_name, last_name FROM authors WHERE last_name = ?')
or die "prepare statement failed: $dbh->errstr()";
$sth->execute('Eggers') or die "execution failed: $dbh->errstr()";
print $sth->rows . " rows found.\n";
while (my $ref = $sth->fetchrow_hashref()) {
print "Found a row: id = $ref->{'id'}, fn = $ref->{'first_name'}\n";
}
$sth->finish;
EXAMPLE
#!/usr/bin/perl
use strict;
use warnings;
use DBI;
# Connect to the database.
my $dbh = DBI->connect("DBI:mysql:database=test;host=localhost",
"joe", "joe's password",
{'RaiseError' => 1});
# Drop table 'foo'. This may fail, if 'foo' doesn't exist
# Thus we put an eval around it.
eval { $dbh->do("DROP TABLE foo") };
print "Dropping foo failed: $@\n" if $@;
# Create a new table 'foo'. This must not fail, thus we don't
# catch errors.
$dbh->do("CREATE TABLE foo (id INTEGER, name VARCHAR(20))");
# INSERT some data into 'foo'. We are using $dbh->quote() for
# quoting the name.
$dbh->do("INSERT INTO foo VALUES (1, " . $dbh->quote("Tim") . ")");
# same thing, but using placeholders (recommended!)
$dbh->do("INSERT INTO foo VALUES (?, ?)", undef, 2, "Jochen");
# now retrieve data from the table.
my $sth = $dbh->prepare("SELECT * FROM foo");
$sth->execute();
while (my $ref = $sth->fetchrow_hashref()) {
print "Found a row: id = $ref->{'id'}, name = $ref->{'name'}\n";
}
$sth->finish();
# Disconnect from the database.
$dbh->disconnect();
DESCRIPTIONDBD::mysql is the Perl5 Database Interface driver for the MySQL
database. In other words: DBD::mysql is an interface between the Perl
programming language and the MySQL programming API that comes with the
MySQL relational database management system. Most functions provided by
this programming API are supported. Some rarely used functions are
missing, mainly because no-one ever requested them. :-)
In what follows we first discuss the use of DBD::mysql, because this is
what you will need the most. For installation, see the separate
document DBD::mysql::INSTALL. See "EXAMPLE" for a simple example
above.
From perl you activate the interface with the statement
use DBI;
After that you can connect to multiple MySQL database servers and send
multiple queries to any of them via a simple object oriented interface.
Two types of objects are available: database handles and statement
handles. Perl returns a database handle to the connect method like so:
$dbh = DBI->connect("DBI:mysql:database=$db;host=$host",
$user, $password, {RaiseError => 1});
Once you have connected to a database, you can execute SQL statements
with:
my $query = sprintf("INSERT INTO foo VALUES (%d, %s)",
$number, $dbh->quote("name"));
$dbh->do($query);
See DBI for details on the quote and do methods. An alternative
approach is
$dbh->do("INSERT INTO foo VALUES (?, ?)", undef,
$number, $name);
in which case the quote method is executed automatically. See also the
bind_param method in DBI. See "DATABASE HANDLES" below for more details
on database handles.
If you want to retrieve results, you need to create a so-called
statement handle with:
$sth = $dbh->prepare("SELECT * FROM $table");
$sth->execute();
This statement handle can be used for multiple things. First of all you
can retrieve a row of data:
my $row = $sth->fetchrow_hashref();
If your table has columns ID and NAME, then $row will be hash ref with
keys ID and NAME. See "STATEMENT HANDLES" below for more details on
statement handles.
But now for a more formal approach:
Class Methods
connect
use DBI;
$dsn = "DBI:mysql:$database";
$dsn = "DBI:mysql:database=$database;host=$hostname";
$dsn = "DBI:mysql:database=$database;host=$hostname;port=$port";
$dbh = DBI->connect($dsn, $user, $password);
The "database" is not a required attribute, but please note that
MySQL has no such thing as a default database. If you don't specify
the database at connection time your active database will be null
and you'd need to prefix your tables with the database name; i.e.
'SELECT * FROM mydb.mytable'.
This is similar to the behavior of the mysql command line client.
Also, 'SELECT DATABASE()' will return the current database active
for the handle.
host
port
The hostname, if not specified or specified as '' or
'localhost', will default to a MySQL server running on the
local machine using the default for the UNIX socket. To connect
to a MySQL server on the local machine via TCP, you must
specify the loopback IP address (127.0.0.1) as the host.
Should the MySQL server be running on a non-standard port
number, you may explicitly state the port number to connect to
in the "hostname" argument, by concatenating the hostname and
port number together separated by a colon ( ":" ) character or
by using the "port" argument.
To connect to a MySQL server on localhost using TCP/IP, you
must specify the hostname as 127.0.0.1 (with the optional
port).
When connecting to a MySQL Server with IPv6, a bracketed IPv6
address should be used. Example DSN:
my $dsn = "DBI:mysql:;host=[1a12:2800:6f2:85::f20:8cf];port=3306";
mysql_client_found_rows
Enables (TRUE value) or disables (FALSE value) the flag
CLIENT_FOUND_ROWS while connecting to the MySQL server. This
has a somewhat funny effect: Without mysql_client_found_rows,
if you perform a query like
UPDATE $table SET id = 1 WHERE id = 1;
then the MySQL engine will always return 0, because no rows
have changed. With mysql_client_found_rows however, it will
return the number of rows that have an id 1, as some people are
expecting. (At least for compatibility to other engines.)
mysql_compression
If your DSN contains the option "mysql_compression=1", then the
communication between client and server will be compressed.
mysql_connect_timeout
If your DSN contains the option "mysql_connect_timeout=##", the
connect request to the server will timeout if it has not been
successful after the given number of seconds.
mysql_write_timeout
If your DSN contains the option "mysql_write_timeout=##", the
write operation to the server will timeout if it has not been
successful after the given number of seconds.
mysql_read_timeout
If your DSN contains the option "mysql_read_timeout=##", the
read operation to the server will timeout if it has not been
successful after the given number of seconds.
mysql_init_command
If your DSN contains the option "mysql_init_command=##", then
this SQL statement is executed when connecting to the MySQL
server. It is automatically re-executed if reconnection
occurs.
mysql_skip_secure_auth
This option is for older mysql databases that don't have secure
auth set.
mysql_read_default_file
mysql_read_default_group
These options can be used to read a config file like
/etc/my.cnf or ~/.my.cnf. By default MySQL's C client library
doesn't use any config files unlike the client programs (mysql,
mysqladmin, ...) that do, but outside of the C client library.
Thus you need to explicitly request reading a config file, as
in
$dsn = "DBI:mysql:test;mysql_read_default_file=/home/joe/my.cnf";
$dbh = DBI->connect($dsn, $user, $password)
The option mysql_read_default_group can be used to specify the
default group in the config file: Usually this is the client
group, but see the following example:
[client]
host=localhost
[perl]
host=perlhost
(Note the order of the entries! The example won't work, if you
reverse the [client] and [perl] sections!)
If you read this config file, then you'll be typically
connected to localhost. However, by using
$dsn = "DBI:mysql:test;mysql_read_default_group=perl;"
. "mysql_read_default_file=/home/joe/my.cnf";
$dbh = DBI->connect($dsn, $user, $password);
you'll be connected to perlhost. Note that if you specify a
default group and do not specify a file, then the default
config files will all be read. See the documentation of the C
function mysql_options() for details.
mysql_socket
It is possible to choose the Unix socket that is used for
connecting to the server. This is done, for example, with
mysql_socket=/dev/mysql
Usually there's no need for this option, unless you are using
another location for the socket than that built into the
client.
mysql_ssl
A true value turns on the CLIENT_SSL flag when connecting to
the MySQL database:
mysql_ssl=1
This means that your communication with the server will be
encrypted.
Please note that this can only work if you enabled SSL when
compiling DBD::mysql; this is the default starting version
4.034. See DBD::mysql::INSTALL for more details.
If you turn mysql_ssl on, you might also wish to use the
following flags:
mysql_ssl_client_key
mysql_ssl_client_cert
mysql_ssl_ca_file
mysql_ssl_ca_path
mysql_ssl_cipher
These are used to specify the respective parameters of a call
to mysql_ssl_set, if mysql_ssl is turned on.
mysql_local_infile
The LOCAL capability for LOAD DATA may be disabled in the MySQL
client library by default. If your DSN contains the option
"mysql_local_infile=1", LOAD DATA LOCAL will be enabled.
(However, this option is *ineffective* if the server has also
been configured to disallow LOCAL.)
mysql_multi_statements
Support for multiple statements separated by a semicolon (;)
may be enabled by using this option. Enabling this option may
cause problems if server-side prepared statements are also
enabled.
mysql_server_prepare
This option is used to enable server side prepared statements.
To use server side prepared statements, all you need to do is
set the variable mysql_server_prepare in the connect:
$dbh = DBI->connect(
"DBI:mysql:database=test;host=localhost;mysql_server_prepare=1",
"",
"",
{ RaiseError => 1, AutoCommit => 1 }
);
or:
$dbh = DBI->connect(
"DBI:mysql:database=test;host=localhost",
"",
"",
{ RaiseError => 1, AutoCommit => 1, mysql_server_prepare => 1 }
);
There are many benefits to using server side prepare
statements, mostly if you are performing many inserts because
of that fact that a single statement is prepared to accept
multiple insert values.
To make sure that the 'make test' step tests whether server
prepare works, you just need to export the env variable
MYSQL_SERVER_PREPARE:
export MYSQL_SERVER_PREPARE=1
Please note that mysql server cannot prepare or execute some
prepared statements. In this case DBD::mysql fallbacks to
normal non-prepared statement and tries again.
mysql_server_prepare_disable_fallback
This option disable fallback to normal non-prepared statement
when mysql server does not support execution of current
statement as prepared.
Useful when you want to be sure that statement is going to be
executed as server side prepared. Error message and code in
case of failure is propagated back to DBI.
mysql_embedded_options
The option <mysql_embedded_options> can be used to pass
'command-line' options to embedded server.
Example:
use DBI;
$testdsn="DBI:mysqlEmb:database=test;mysql_embedded_options=--help,--verbose";
$dbh = DBI->connect($testdsn,"a","b");
This would cause the command line help to the embedded MySQL
server library to be printed.
mysql_embedded_groups
The option <mysql_embedded_groups> can be used to specify the
groups in the config file(my.cnf) which will be used to get
options for embedded server. If not specified [server] and
[embedded] groups will be used.
Example:
$testdsn="DBI:mysqlEmb:database=test;mysql_embedded_groups=embedded_server,common";
mysql_conn_attrs
The option <mysql_conn_attrs> is a hash of attribute names and
values which can be used to send custom connection attributes
to the server. Some attributes like '_os', '_platform',
'_client_name' and '_client_version' are added by
libmysqlclient and 'program_name' is added by DBD::mysql.
You can then later read these attributes from the performance
schema tables which can be quite helpful for profiling your
database or creating statistics. You'll have to use a MySQL
5.6 server and libmysqlclient or newer to leverage this
feature.
my $dbh= DBI->connect($dsn, $user, $password,
{ AutoCommit => 0,
mysql_conn_attrs => {
foo => 'bar',
wiz => 'bang'
},
});
Now you can select the results from the performance schema
tables. You can do this in the same session, but also
afterwards. It can be very useful to answer questions like
'which script sent this query?'.
my $results = $dbh->selectall_hashref(
'SELECT * FROM performance_schema.session_connect_attrs',
'ATTR_NAME'
);
This returns:
$result = {
'foo' => {
'ATTR_VALUE' => 'bar',
'PROCESSLIST_ID' => '3',
'ATTR_NAME' => 'foo',
'ORDINAL_POSITION' => '6'
},
'wiz' => {
'ATTR_VALUE' => 'bang',
'PROCESSLIST_ID' => '3',
'ATTR_NAME' => 'wiz',
'ORDINAL_POSITION' => '3'
},
'program_name' => {
'ATTR_VALUE' => './foo.pl',
'PROCESSLIST_ID' => '3',
'ATTR_NAME' => 'program_name',
'ORDINAL_POSITION' => '5'
},
'_client_name' => {
'ATTR_VALUE' => 'libmysql',
'PROCESSLIST_ID' => '3',
'ATTR_NAME' => '_client_name',
'ORDINAL_POSITION' => '1'
},
'_client_version' => {
'ATTR_VALUE' => '5.6.24',
'PROCESSLIST_ID' => '3',
'ATTR_NAME' => '_client_version',
'ORDINAL_POSITION' => '7'
},
'_os' => {
'ATTR_VALUE' => 'osx10.8',
'PROCESSLIST_ID' => '3',
'ATTR_NAME' => '_os',
'ORDINAL_POSITION' => '0'
},
'_pid' => {
'ATTR_VALUE' => '59860',
'PROCESSLIST_ID' => '3',
'ATTR_NAME' => '_pid',
'ORDINAL_POSITION' => '2'
},
'_platform' => {
'ATTR_VALUE' => 'x86_64',
'PROCESSLIST_ID' => '3',
'ATTR_NAME' => '_platform',
'ORDINAL_POSITION' => '4'
}
};
Private MetaData Methods
ListDBs
my $drh = DBI->install_driver("mysql");
@dbs = $drh->func("$hostname:$port", '_ListDBs');
@dbs = $drh->func($hostname, $port, '_ListDBs');
@dbs = $dbh->func('_ListDBs');
Returns a list of all databases managed by the MySQL server running
on $hostname, port $port. This is a legacy method. Instead, you
should use the portable method
@dbs = DBI->data_sources("mysql");
DATABASE HANDLES
The DBD::mysql driver supports the following attributes of database
handles (read only):
$errno = $dbh->{'mysql_errno'};
$error = $dbh->{'mysql_error'};
$info = $dbh->{'mysql_hostinfo'};
$info = $dbh->{'mysql_info'};
$insertid = $dbh->{'mysql_insertid'};
$info = $dbh->{'mysql_protoinfo'};
$info = $dbh->{'mysql_serverinfo'};
$info = $dbh->{'mysql_stat'};
$threadId = $dbh->{'mysql_thread_id'};
These correspond to mysql_errno(), mysql_error(),
mysql_get_host_info(), mysql_info(), mysql_insert_id(),
mysql_get_proto_info(), mysql_get_server_info(), mysql_stat() and
mysql_thread_id(), respectively.
mysql_clientinfo
List information of the MySQL client library that DBD::mysql was
built against:
print "$dbh->{mysql_clientinfo}\n";
5.2.0-MariaDB
mysql_clientversion
print "$dbh->{mysql_clientversion}\n";
50200
mysql_serverversion
print "$dbh->{mysql_serverversion}\n";
50200
mysql_dbd_stats
$info_hashref = $dhb->{mysql_dbd_stats};
DBD::mysql keeps track of some statistics in the mysql_dbd_stats
attribute. The following stats are being maintained:
auto_reconnects_ok
The number of times that DBD::mysql successfully reconnected
to the mysql server.
auto_reconnects_failed
The number of times that DBD::mysql tried to reconnect to
mysql but failed.
The DBD::mysql driver also supports the following attributes of
database handles (read/write):
mysql_auto_reconnect
This attribute determines whether DBD::mysql will automatically
reconnect to mysql if the connection be lost. This feature defaults
to off; however, if either the GATEWAY_INTERFACE or MOD_PERL
environment variable is set, DBD::mysql will turn
mysql_auto_reconnect on. Setting mysql_auto_reconnect to on is not
advised if 'lock tables' is used because if DBD::mysql reconnect to
mysql all table locks will be lost. This attribute is ignored when
AutoCommit is turned off, and when AutoCommit is turned off,
DBD::mysql will not automatically reconnect to the server.
It is also possible to set the default value of the
"mysql_auto_reconnect" attribute for the $dbh by passing it in the
"\%attr" hash for "DBI-"connect>.
$dbh->{mysql_auto_reconnect} = 1;
or
my $dbh = DBI->connect($dsn, $user, $password, {
mysql_auto_reconnect => 1,
});
Note that if you are using a module or framework that performs
reconnections for you (for example DBIx::Connector in fixup mode),
this value must be set to 0.
mysql_use_result
This attribute forces the driver to use mysql_use_result rather
than mysql_store_result. The former is faster and less memory
consuming, but tends to block other processes. mysql_store_result
is the default due to that fact storing the result is expected
behavior with most applications.
It is possible to set the default value of the "mysql_use_result"
attribute for the $dbh via the DSN:
$dbh = DBI->connect("DBI:mysql:test;mysql_use_result=1", "root", "");
You can also set it after creation of the database handle:
$dbh->{mysql_use_result} = 0; # disable
$dbh->{mysql_use_result} = 1; # enable
You can also set or unset the "mysql_use_result" setting on your
statement handle, when creating the statement handle or after it
has been created. See "STATEMENT HANDLES".
mysql_enable_utf8
This attribute determines whether DBD::mysql should assume strings
stored in the database are utf8. This feature defaults to off.
When set, a data retrieved from a textual column type (char,
varchar, etc) will have the UTF-8 flag turned on if necessary.
This enables character semantics on that string. You will also
need to ensure that your database / table / column is configured to
use UTF8. See for more information the chapter on character set
support in the MySQL manual:
<http://dev.mysql.com/doc/refman/5.7/en/charset.html>
Additionally, turning on this flag tells MySQL that incoming data
should be treated as UTF-8. This will only take effect if used as
part of the call to connect(). If you turn the flag on after
connecting, you will need to issue the command "SET NAMES utf8" to
get the same effect.
mysql_enable_utf8mb4
This is similar to mysql_enable_utf8, but is capable of handling
4-byte UTF-8 characters.
mysql_bind_type_guessing
This attribute causes the driver (emulated prepare statements) to
attempt to guess if a value being bound is a numeric value, and if
so, doesn't quote the value. This was created by Dragonchild and
is one way to deal with the performance issue of using quotes in a
statement that is inserting or updating a large numeric value. This
was previously called "unsafe_bind_type_guessing" because it is
experimental. I have successfully run the full test suite with this
option turned on, the name can now be simply
"mysql_bind_type_guessing".
CAVEAT: Even though you can insert an integer value into a
character column, if this column is indexed, if you query that
column with the integer value not being quoted, it will not use the
index:
MariaDB [test]> explain select * from test where value0 = '3' \G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: test
type: ref
possible_keys: value0
key: value0
key_len: 13
ref: const
rows: 1
Extra: Using index condition
1 row in set (0.00 sec)
MariaDB [test]> explain select * from test where value0 = 3
-> \G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: test
type: ALL
possible_keys: value0
key: NULL
key_len: NULL
ref: NULL
rows: 6
Extra: Using where
1 row in set (0.00 sec)
See bug: https://rt.cpan.org/Ticket/Display.html?id=43822
"mysql_bind_type_guessing" can be turned on via
- through DSN
my $dbh= DBI->connect('DBI:mysql:test', 'username', 'pass',
{ mysql_bind_type_guessing => 1})
- OR after handle creation
$dbh->{mysql_bind_type_guessing} = 1;
mysql_bind_comment_placeholders
This attribute causes the driver (emulated prepare statements) will
cause any placeholders in comments to be bound. This is not correct
prepared statement behavior, but some developers have come to
depend on this behavior, so I have made it available in 4.015
mysql_no_autocommit_cmd
This attribute causes the driver to not issue 'set autocommit'
either through explicit or using mysql_autocommit(). This is
particularly useful in the case of using MySQL Proxy.
See the bug report:
https://rt.cpan.org/Public/Bug/Display.html?id=46308
"mysql_no_autocommit_cmd" can be turned on when creating the
database handle:
my $dbh = DBI->connect('DBI:mysql:test', 'username', 'pass',
{ mysql_no_autocommit_cmd => 1});
or using an existing database handle:
$dbh->{mysql_no_autocommit_cmd} = 1;
ping
This can be used to send a ping to the server.
$rc = $dbh->ping();
STATEMENT HANDLES
The statement handles of DBD::mysql support a number of attributes. You
access these by using, for example,
my $numFields = $sth->{NUM_OF_FIELDS};
Note, that most attributes are valid only after a successful execute.
An "undef" value will returned otherwise. The most important exception
is the "mysql_use_result" attribute, which forces the driver to use
mysql_use_result rather than mysql_store_result. The former is faster
and less memory consuming, but tends to block other processes. (That's
why mysql_store_result is the default.)
To set the "mysql_use_result" attribute, use either of the following:
my $sth = $dbh->prepare("QUERY", { mysql_use_result => 1});
or
my $sth = $dbh->prepare($sql);
$sth->{mysql_use_result} = 1;
Column dependent attributes, for example NAME, the column names, are
returned as a reference to an array. The array indices are
corresponding to the indices of the arrays returned by fetchrow and
similar methods. For example the following code will print a header of
table names together with all rows:
my $sth = $dbh->prepare("SELECT * FROM $table") ||
die "Error:" . $dbh->errstr . "\n";
$sth->execute || die "Error:" . $sth->errstr . "\n";
my $names = $sth->{NAME};
my $numFields = $sth->{'NUM_OF_FIELDS'} - 1;
for my $i ( 0..$numFields ) {
printf("%s%s", $i ? "," : "", $$names[$i]);
}
print "\n";
while (my $ref = $sth->fetchrow_arrayref) {
for my $i ( 0..$numFields ) {
printf("%s%s", $i ? "," : "", $$ref[$i]);
}
print "\n";
}
For portable applications you should restrict yourself to attributes
with capitalized or mixed case names. Lower case attribute names are
private to DBD::mysql. The attribute list includes:
ChopBlanks
this attribute determines whether a fetchrow will chop preceding
and trailing blanks off the column values. Chopping blanks does not
have impact on the max_length attribute.
mysql_insertid
If the statement you executed performs an INSERT, and there is an
AUTO_INCREMENT column in the table you inserted in, this attribute
holds the value stored into the AUTO_INCREMENT column, if that
value is automatically generated, by storing NULL or 0 or was
specified as an explicit value.
Typically, you'd access the value via $sth->{mysql_insertid}. The
value can also be accessed via $dbh->{mysql_insertid} but this can
easily produce incorrect results in case one database handle is
shared.
mysql_is_blob
Reference to an array of boolean values; TRUE indicates, that the
respective column is a blob. This attribute is valid for MySQL
only.
mysql_is_key
Reference to an array of boolean values; TRUE indicates, that the
respective column is a key. This is valid for MySQL only.
mysql_is_num
Reference to an array of boolean values; TRUE indicates, that the
respective column contains numeric values.
mysql_is_pri_key
Reference to an array of boolean values; TRUE indicates, that the
respective column is a primary key.
mysql_is_auto_increment
Reference to an array of boolean values; TRUE indicates that the
respective column is an AUTO_INCREMENT column. This is only valid
for MySQL.
mysql_length
mysql_max_length
A reference to an array of maximum column sizes. The max_length is
the maximum physically present in the result table, length gives
the theoretically possible maximum. max_length is valid for MySQL
only.
NAME
A reference to an array of column names.
NULLABLE
A reference to an array of boolean values; TRUE indicates that this
column may contain NULL's.
NUM_OF_FIELDS
Number of fields returned by a SELECT or LISTFIELDS statement. You
may use this for checking whether a statement returned a result: A
zero value indicates a non-SELECT statement like INSERT, DELETE or
UPDATE.
mysql_table
A reference to an array of table names, useful in a JOIN result.
TYPE
A reference to an array of column types. The engine's native column
types are mapped to portable types like DBI::SQL_INTEGER() or
DBI::SQL_VARCHAR(), as good as possible. Not all native types have
a meaningful equivalent, for example
DBD::mysql::FIELD_TYPE_INTERVAL is mapped to DBI::SQL_VARCHAR().
If you need the native column types, use mysql_type. See below.
mysql_type
A reference to an array of MySQL's native column types, for example
DBD::mysql::FIELD_TYPE_SHORT() or DBD::mysql::FIELD_TYPE_STRING().
Use the TYPE attribute, if you want portable types like
DBI::SQL_SMALLINT() or DBI::SQL_VARCHAR().
mysql_type_name
Similar to mysql, but type names and not numbers are returned.
Whenever possible, the ANSI SQL name is preferred.
mysql_warning_count
The number of warnings generated during execution of the SQL
statement. This attribute is available on both statement handles
and database handles.
TRANSACTION SUPPORT
The transaction support works as follows:
· By default AutoCommit mode is on, following the DBI specifications.
· If you execute
$dbh->{AutoCommit} = 0;
or
$dbh->{AutoCommit} = 1;
then the driver will set the MySQL server variable autocommit to 0
or 1, respectively. Switching from 0 to 1 will also issue a COMMIT,
following the DBI specifications.
· The methods
$dbh->rollback();
$dbh->commit();
will issue the commands ROLLBACK and COMMIT, respectively. A
ROLLBACK will also be issued if AutoCommit mode is off and the
database handles DESTROY method is called. Again, this is following
the DBI specifications.
Given the above, you should note the following:
· You should never change the server variable autocommit manually,
unless you are ignoring DBI's transaction support.
· Switching AutoCommit mode from on to off or vice versa may fail.
You should always check for errors when changing AutoCommit mode.
The suggested way of doing so is using the DBI flag RaiseError. If
you don't like RaiseError, you have to use code like the following:
$dbh->{AutoCommit} = 0;
if ($dbh->{AutoCommit}) {
# An error occurred!
}
· If you detect an error while changing the AutoCommit mode, you
should no longer use the database handle. In other words, you
should disconnect and reconnect again, because the transaction mode
is unpredictable. Alternatively you may verify the transaction mode
by checking the value of the server variable autocommit. However,
such behaviour isn't portable.
· DBD::mysql has a "reconnect" feature that handles the so-called
MySQL "morning bug": If the server has disconnected, most probably
due to a timeout, then by default the driver will reconnect and
attempt to execute the same SQL statement again. However, this
behaviour is disabled when AutoCommit is off: Otherwise the
transaction state would be completely unpredictable after a
reconnect.
· The "reconnect" feature of DBD::mysql can be toggled by using the
mysql_auto_reconnect attribute. This behaviour should be turned off
in code that uses LOCK TABLE because if the database server time
out and DBD::mysql reconnect, table locks will be lost without any
indication of such loss.
MULTIPLE RESULT SETSDBD::mysql supports multiple result sets, thanks to Guy Harrison!
The basic usage of multiple result sets is
do
{
while (@row = $sth->fetchrow_array())
{
do stuff;
}
} while ($sth->more_results)
An example would be:
$dbh->do("drop procedure if exists someproc") or print $DBI::errstr;
$dbh->do("create procedure someproc() deterministic
begin
declare a,b,c,d int;
set a=1;
set b=2;
set c=3;
set d=4;
select a, b, c, d;
select d, c, b, a;
select b, a, c, d;
select c, b, d, a;
end") or print $DBI::errstr;
$sth=$dbh->prepare('call someproc()') ||
die $DBI::err.": ".$DBI::errstr;
$sth->execute || die DBI::err.": ".$DBI::errstr; $rowset=0;
do {
print "\nRowset ".++$i."\n---------------------------------------\n\n";
foreach $colno (0..$sth->{NUM_OF_FIELDS}-1) {
print $sth->{NAME}->[$colno]."\t";
}
print "\n";
while (@row= $sth->fetchrow_array()) {
foreach $field (0..$#row) {
print $row[$field]."\t";
}
print "\n";
}
} until (!$sth->more_results)
Issues with multiple result sets
Please be aware there could be issues if your result sets are "jagged",
meaning the number of columns of your results vary. Varying numbers of
columns could result in your script crashing.
MULTITHREADING
The multithreading capabilities of DBD::mysql depend completely on the
underlying C libraries. The modules are working with handle data only,
no global variables are accessed or (to the best of my knowledge)
thread unsafe functions are called. Thus DBD::mysql is believed to be
completely thread safe, if the C libraries are thread safe and you
don't share handles among threads.
The obvious question is: Are the C libraries thread safe? In the case
of MySQL the answer is "mostly" and, in theory, you should be able to
get a "yes", if the C library is compiled for being thread safe (By
default it isn't.) by passing the option -with-thread-safe-client to
configure. See the section on How to make a threadsafe client in the
manual.
ASYNCHRONOUS QUERIES
You can make a single asynchronous query per MySQL connection; this
allows you to submit a long-running query to the server and have an
event loop inform you when it's ready. An asynchronous query is
started by either setting the 'async' attribute to a true value in the
"do" in DBI method, or in the "prepare" in DBI method. Statements
created with 'async' set to true in prepare always run their queries
asynchronously when "execute" in DBI is called. The driver also offers
three additional methods: "mysql_async_result", "mysql_async_ready",
and "mysql_fd". "mysql_async_result" returns what do or execute would
have; that is, the number of rows affected. "mysql_async_ready"
returns true if "mysql_async_result" will not block, and zero
otherwise. They both return "undef" if that handle is not currently
running an asynchronous query. "mysql_fd" returns the file descriptor
number for the MySQL connection; you can use this in an event loop.
Here's an example of how to use the asynchronous query interface:
use feature 'say';
$dbh->do('SELECT SLEEP(10)', { async => 1 });
until($dbh->mysql_async_ready) {
say 'not ready yet!';
sleep 1;
}
my $rows = $dbh->mysql_async_result;
INSTALLATION
See DBD::mysql::INSTALL.
AUTHORS
Originally, there was a non-DBI driver, Mysql, which was much like PHP
drivers such as mysql and mysqli. The Mysql module was originally
written by Andreas König <koenig@kulturbox.de> who still, to this day,
contributes patches to DBD::mysql. An emulated version of Mysql was
provided to DBD::mysql from Jochen Wiedmann, but eventually deprecated
as it was another bundle of code to maintain.
The first incarnation of DBD::mysql was developed by Alligator
Descartes, who was also aided and abetted by Gary Shea, Andreas König
and Tim Bunce.
The current incarnation of DBD::mysql was written by Jochen Wiedmann,
then numerous changes and bug-fixes were added by Rudy Lippan. Next,
prepared statement support was added by Patrick Galbraith and Alexy
Stroganov (who also solely added embedded server support).
For the past nine years DBD::mysql has been maintained by Patrick
Galbraith (patg@patg.net), and recently with the great help of Michiel
Beijen (michiel.beijen@gmail.com), along with the entire community of
Perl developers who keep sending patches to help continue improving
DBD::mysqlCONTRIBUTIONS
Anyone who desires to contribute to this project is encouraged to do
so. Currently, the source code for this project can be found at
Github:
<https://github.com/perl5-dbi/DBD-mysql/>
Either fork this repository and produce a branch with your changeset
that the maintainer can merge to his tree, or create a diff with git.
The maintainer is more than glad to take contributions from the
community as many features and fixes from DBD::mysql have come from the
community.
COPYRIGHT
This module is
· Large Portions Copyright (c) 2004-2013 Patrick Galbraith
· Large Portions Copyright (c) 2004-2006 Alexey Stroganov
· Large Portions Copyright (c) 2003-2005 Rudolf Lippan
· Large Portions Copyright (c) 1997-2003 Jochen Wiedmann, with code
portions
· Copyright (c)1994-1997 their original authors
LICENSE
This module is released under the same license as Perl itself. See
<http://www.perl.com/perl/misc/Artistic.html> for details.
MAILING LIST SUPPORT
This module is maintained and supported on a mailing list, dbi-users.
To subscribe to this list, send an email to
dbi-users-subscribe@perl.org
Mailing list archives are at
<http://groups.google.com/group/perl.dbi.users?hl=en&lr=>
ADDITIONAL DBI INFORMATION
Additional information on the DBI project can be found on the World
Wide Web at the following URL:
<http://dbi.perl.org>
where documentation, pointers to the mailing lists and mailing list
archives and pointers to the most current versions of the modules can
be used.
Information on the DBI interface itself can be gained by typing:
perldoc DBI
Information on DBD::mysql specifically can be gained by typing:
perldoc DBD::mysql
(this will display the document you're currently reading)
BUG REPORTING, ENHANCEMENT/FEATURE REQUESTS
Please report bugs, including all the information needed such as
DBD::mysql version, MySQL version, OS type/version, etc to this link:
<https://rt.cpan.org/Dist/Display.html?Name=DBD-mysql>
Note: until recently, MySQL/Sun/Oracle responded to bugs and assisted
in fixing bugs which many thanks should be given for their help! This
driver is outside the realm of the numerous components they support,
and the maintainer and community solely support DBD::mysqlperl v5.26.0 2017-07-22 DBD::mysql(3pm)
