DBD::mysql (3)

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NAME

DBD::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();

DESCRIPTION

DBD::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 that comes with the MySQL relational database management system. Most functions provided by this programming 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 ``

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

statements with:

  my $query = sprintf("INSERT INTO foo VALUES (%d, %s)",
                      $number, $dbh->quote("name"));
  $dbh->do($query);

See

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

. See `` 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

and then $row will be hash ref with keys and See `` 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: <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: 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:

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

, 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 SETS

DBD::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 method, or in the ``prepare'' in method. Statements created with 'async' set to true in prepare always run their queries asynchronously when ``execute'' in 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 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::mysql

CONTRIBUTIONS

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:

<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 <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

<groups.google.com/group/perl.dbi.users?hl=en&lr=>

ADDITIONAL DBI INFORMATION

Additional information on the project can be found on the World Wide Web at the following

<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

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, type/version, etc to this link:

<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::mysql