NAME
    DBD::CSV - DBI driver for CSV files

SYNOPSIS
        use DBI;
        $dbh = DBI->connect("DBI:CSV:f_dir=/home/joe/csvdb")
            or die "Cannot connect: " . $DBI::errstr;
        $sth = $dbh->prepare("CREATE TABLE a (id INTEGER, name CHAR(10))")
            or die "Cannot prepare: " . $dbh->errstr();
        $sth->execute() or die "Cannot execute: " . $sth->errstr();
        $sth->finish();
        $dbh->disconnect();

        # Read a CSV file with ";" as the separator, as exported by
        # MS Excel. Note we need to escape the ";", otherwise it
        # would be treated as an attribute separator.
        $dbh = DBI->connect(qq{DBI:CSV:csv_sep_char=\\;});
        $sth = $dbh->prepare("SELECT * FROM info");

        # Same example, this time reading "info.csv" as a table:
        $dbh = DBI->connect(qq{DBI:CSV:csv_sep_char=\\;});
        $dbh->{'csv_tables'}->{'info'} = { 'file' => 'info.csv'};
        $sth = $dbh->prepare("SELECT * FROM info");

WARNING
    THIS IS ALPHA SOFTWARE. It is *only* 'Alpha' because the
    interface (API) is not finalized. The Alpha status does not
    reflect code quality or stability.

DESCRIPTION
    The DBD::CSV module is yet another driver for the DBI (Database
    independent interface for Perl). This one is based on the SQL
    "engine" SQL::Statement and the abstract DBI driver DBD::File
    and implements access to so-called CSV files (Comma separated
    values). Such files are mostly used for exporting MS Access and
    MS Excel data.

    See the DBI(3) manpage for details on DBI, the SQL::Statement(3)
    manpage for details on SQL::Statement and the DBD::File(3)
    manpage for details on the base class DBD::File.

  Prerequisites

    The only system dependent feature that DBD::File uses, is the
    `flock()' function. Thus the module should run (in theory) on
    any system with a working `flock()', in particular on all Unix
    machines and on Windows NT. Under Windows 95 and MacOS the use
    of `flock()' is disabled, thus the module should still be
    usable,

    Unlike other DBI drivers, you don't need an external SQL engine
    or a running server. All you need are the following Perl
    modules, available from any CPAN mirror, for example

      ftp://ftp.funet.fi/pub/languages/perl/CPAN/modules/by-module

    DBI the DBI (Database independent interface for Perl), version 1.00
        or a later release

    SQL::Statement
        a simple SQL engine

    Text::CSV_XS
        this module is used for writing rows to or reading rows from
        CSV files.

  Installation

    Installing this module (and the prerequisites from above) is
    quite simple. You just fetch the archive, extract it with

        gzip -cd DBD-CSV-0.1000.tar.gz | tar xf -

    (this is for Unix users, Windows users would prefer WinZip or
    something similar) and then enter the following:

        cd DBD-CSV-0.1000
        perl Makefile.PL
        make
        make test

    If any tests fail, let me know. Otherwise go on with

        make install

    Note that you almost definitely need root or administrator
    permissions. If you don't have them, read the
    ExtUtils::MakeMaker man page for details on installing in your
    own directories. the ExtUtils::MakeMaker manpage.

  Creating a database handle

    Creating a database handle usually implies connecting to a
    database server. Thus this command reads

        use DBI;
        my $dbh = DBI->connect("DBI:CSV:f_dir=$dir");

    The directory tells the driver where it should create or open
    tables (a.k.a. files). It defaults to the current directory,
    thus the following are equivalent:

        $dbh = DBI->connect("DBI:CSV:");
        $dbh = DBI->connect("DBI:CSV:f_dir=.");

    (I was told, that VMS requires

        $dbh = DBI->connect("DBI:CSV:f_dir=");

    for whatever reasons.)

    You may set other attributes in the DSN string, separated by
    semicolons.

  Creating and dropping tables

    You can create and drop tables with commands like the following:

        $dbh->do("CREATE TABLE $table (id INTEGER, name CHAR(64))");
        $dbh->do("DROP TABLE $table");

    Note that currently only the column names will be stored and no
    other data. Thus all other information including column type
    (INTEGER or CHAR(x), for example), column attributes (NOT NULL,
    PRIMARY KEY, ...) will silently be discarded. This may change in
    a later release.

    A drop just removes the file without any warning.

    See the DBI(3) manpage for more details.

    Table names cannot be arbitrary, due to restrictions of the SQL
    syntax. I recommend that table names are valid SQL identifiers:
    The first character is alphabetic, followed by an arbitrary
    number of alphanumeric characters. If you want to use other
    files, the file names must start with '/', './' or '../' and
    they must not contain white space.

  Inserting, fetching and modifying data

    The following examples insert some data in a table and fetch it
    back: First all data in the string:

        $dbh->do("INSERT INTO $table VALUES (1, "
                 . $dbh->quote("foobar") . ")");

    Note the use of the quote method for escaping the word 'foobar'.
    Any string must be escaped, even if it doesn't contain binary
    data.

    Next an example using parameters:

        $dbh->do("INSERT INTO $table VALUES (?, ?)", undef,
                 2, "It's a string!");

    Note that you don't need to use the quote method here, this is
    done automatically for you. This version is particularly well
    designed for loops. Whenever performance is an issue, I
    recommend using this method.

    You might wonder about the `undef'. Don't wonder, just take it
    as it is. :-) It's an attribute argument that I have never ever
    used and will be parsed to the prepare method as a second
    argument.

    To retrieve data, you can use the following:

        my($query) = "SELECT * FROM $table WHERE id > 1 ORDER BY id";
        my($sth) = $dbh->prepare($query);
        $sth->execute();
        while (my $row = $sth->fetchrow_hashref) {
            print("Found result row: id = ", $row->{'id'},
                  ", name = ", $row->{'name'});
        }
        $sth->finish();

    Again, column binding works: The same example again.

        my($query) = "SELECT * FROM $table WHERE id > 1 ORDER BY id";
        my($sth) = $dbh->prepare($query);
        $sth->execute();
        my($id, $name);
        $sth->bind_columns(undef, \$id, \$name);
        while ($sth->fetch) {
            print("Found result row: id = $id, name = $name\n");
        }
        $sth->finish();

    Of course you can even use input parameters. Here's the same
    example for the third time:

        my($query) = "SELECT * FROM $table WHERE id = ?";
        my($sth) = $dbh->prepare($query);
        $sth->bind_columns(undef, \$id, \$name);
        for (my($i) = 1;  $i <= 2;   $i++) {
            $sth->execute($id);
            if ($sth->fetch) {
                print("Found result row: id = $id, name = $name\n");
            }
            $sth->finish();
        }

    See the DBI(3) manpage for details on these methods. See the
    SQL::Statement(3) manpage for details on the WHERE clause.

    Data rows are modified with the UPDATE statement:

        $dbh->do("UPDATE $table SET id = 3 WHERE id = 1");

    Likewise you use the DELETE statement for removing rows:

        $dbh->do("DELETE FROM $table WHERE id > 1");

  Error handling

    In the above examples we have never cared about return codes. Of
    course, this cannot be recommended. Instead we should have
    written (for example):

        my($query) = "SELECT * FROM $table WHERE id = ?";
        my($sth) = $dbh->prepare($query)
            or die "prepare: " . $dbh->errstr();
        $sth->bind_columns(undef, \$id, \$name)
            or die "bind_columns: " . $dbh->errstr();
        for (my($i) = 1;  $i <= 2;   $i++) {
            $sth->execute($id)
                or die "execute: " . $dbh->errstr();
            if ($sth->fetch) {
                print("Found result row: id = $id, name = $name\n");
            }
        }
        $sth->finish($id)
            or die "finish: " . $dbh->errstr();

    Obviously this is tedious. Fortunately we have DBI's
    *RaiseError* attribute:

        $dbh->{'RaiseError'} = 1;
        $@ = '';
        eval {
            my($query) = "SELECT * FROM $table WHERE id = ?";
            my($sth) = $dbh->prepare($query);
            $sth->bind_columns(undef, \$id, \$name);
            for (my($i) = 1;  $i <= 2;   $i++) {
                $sth->execute($id);
                if ($sth->fetch) {
                    print("Found result row: id = $id, name = $name\n");
                }
            }
            $sth->finish($id);
        };
        if ($@) { die "SQL database error: $@"; }

    This is not only shorter, it even works when using DBI methods
    within subroutines.

  Metadata

    The following attributes are handled by DBI itself and not by
    DBD::File, thus they all work as expected:

        Active
        ActiveKids
        CachedKids
        CompatMode             (Not used)
        InactiveDestroy
        Kids
        PrintError
        RaiseError
        Warn                   (Not used)

    The following DBI attributes are handled by DBD::File:

    AutoCommit
        Always on

    ChopBlanks
        Works

    NUM_OF_FIELDS
        Valid after `$sth->execute'

    NUM_OF_PARAMS
        Valid after `$sth->prepare'

    NAME
        Valid after `$sth->execute'; undef for Non-Select
        statements.

    NULLABLE
        Not really working. Always returns an array ref of one's, as
        DBD::CSV doesn't verify input data. Valid after `$sth-
        >execute'; undef for non-Select statements.

    These attributes and methods are not supported:

        bind_param_inout
        CursorName
        LongReadLen
        LongTruncOk

    In addition to the DBI attributes, you can use the following dbh
    attributes:

    f_dir   This attribute is used for setting the directory where CSV
            files are opened. Usually you set it in the dbh, it
            defaults to the current directory ("."). However, it is
            overwritable in the statement handles.

    csv_eol
    csv_sep_char
    csv_quote_char
    csv_escape_char
    csv_class
    csv_csv The attributes *csv_eol*, *csv_sep_char*, *csv_quote_char*
            and *csv_escape_char* are corresponding to the
            respective attributes of the Text::CSV_XS object. You
            want to set these attributes if you have unusual CSV
            files like /etc/passwd or MS Excel generated CSV files
            with a semicolon as separator. Defaults are "\015\012",
            ';', '"' and '"', respectively.

            The attributes are used to create an instance of the
            class *csv_class*, by default Text::CSV_XS.
            Alternatively you may pass an instance as *csv_csv*, the
            latter takes precedence. Note that the *binary*
            attribute *must* be set to a true value in that case.

            Additionally you may overwrite these attributes on a
            per-table base in the *csv_tables* attribute.

    csv_tables
            This hash ref is used for storing table dependent
            metadata. For any table it contains an element with the
            table name as key and another hash ref with the
            following attributes:

    file                The tables file name; defaults to

                            "$dbh->{f_dir}/$table"

    eol
    sep_char
    quote_char
    escape_char
    class
    csv                 These correspond to the attributes *csv_eol*,
                        *csv_sep_char*, *csv_quote_char*,
                        *csv_escape_char*, *csv_class* and
                        *csv_csv*. The difference is that they work
                        on a per-table base.

    col_names
    skip_first_row      By default DBD::CSV assumes that column names
                        are stored in the first row of the CSV file.
                        If this is not the case, you can supply an
                        array ref of table names with the
                        *col_names* attribute. In that case the
                        attribute *skip_first_row* will be set to
                        FALSE.

                        If you supply an empty array ref, the driver
                        will read the first row for you, count the
                        number of columns and create column names
                        like `col0', `col1', ...

    Example: Suggest you want to use /etc/passwd as a CSV file. :-)
    There simplest way is:

        require DBI;
        my $dbh = DBI->connect("DBI:CSV:f_dir=/etc;csv_eol=\n;"
                               . "csv_sep_char=:;csv_quote_char=;"
                               . "csv_escape_char=");
        $dbh->{'csv_tables'}->{'passwd'} = {
            'col_names' => ["login", "password", "uid", "gid", "realname",
                            "directory", "shell"]
        };
        $sth = $dbh->prepare("SELECT * FROM passwd");

    Another possibility where you leave all the defaults as they are
    and overwrite them on a per table base:

        require DBI;
        my $dbh = DBI->connect("DBI:CSV:");
        $dbh->{'csv_tables'}->{'passwd'} = {
            'eol' => "\n",
            'sep_char' => ":",
            'quote_char' => undef,
            'escape_char' => undef,
            'file' => '/etc/passwd',
            'col_names' => ["login", "password", "uid", "gid", "realname",
                            "directory", "shell"]
        };
        $sth = $dbh->prepare("SELECT * FROM passwd");

  Driver private methods

    These methods are inherited from DBD::File:

    data_sources
        The `data_sources' method returns a list of subdirectories
        of the current directory in the form
        "DBI:CSV:directory=$dirname".

        If you want to read the subdirectories of another directory,
        use

            my($drh) = DBI->install_driver("CSV");
            my(@list) = $drh->data_sources('f_dir' => '/usr/local/csv_data' );

    list_tables
        This method returns a list of file names inside $dbh-
        >{'directory'}. Example:

            my($dbh) = DBI->connect("DBI:CSV:directory=/usr/local/csv_data");
            my(@list) = $dbh->func('list_tables');

        Note that the list includes all files contained in the
        directory, even those that have non-valid table names, from
        the view of SQL. See the section on "Creating and dropping
        tables" above.

  Data restrictions

    When inserting and fetching data, you will sometimes be
    surprised: DBD::CSV doesn't correctly handle data types, in
    particular NULLs. If you insert integers, it might happen, that
    fetch returns a string. Of course, a string containing the
    integer, so that's perhaps not a real problem. But the following
    will never work:

        $dbh->do("INSERT INTO $table (id, name) VALUES (?, ?)",
                 undef, "foo bar");
        $sth = $dbh->prepare("SELECT * FROM $table WHERE id IS NULL");
        $sth->execute();
        my($id, $name);
        $sth->bind_columns(undef, \$id, \$name);
        while ($sth->fetch) {
            printf("Found result row: id = %s, name = %s\n",
                  defined($id) ? $id : "NULL",
                  defined($name) ? $name : "NULL");
        }
        $sth->finish();

    The row we have just inserted, will never be returned! The
    reason is obvious, if you examine the CSV file: The
    corresponding row looks like

        "","foo bar"

    In other words, not a NULL is stored, but an empty string. CSV
    files don't have a concept of NULL values. Surprisingly the
    above example works, if you insert a NULL value for the name!
    Again, you find the explanation by examining the CSV file:

        ""

    In other words, DBD::CSV has "emulated" a NULL value by writing
    a row with less columns. Of course this works only if the
    rightmost column is NULL, the two rightmost columns are NULL,
    ..., but the leftmost column will never be NULL!

    See the section on "Creating and dropping tables" above for
    table name restrictions.

TODO
    Extensions of DBD::CSV:

    CSV file scanner
        Write a simple CSV file scanner that reads a CSV file and
        attempts to guess sep_char, quote_char, escape_char and eol
        automatically.

    These are merely restrictions of the DBD::File or SQL::Statement
    modules:

    Joins
        The current version of the module works with single table
        SELECTs only, although the basic design of the
        SQL::Statement module allows joins and the like.

    Table name mapping
        Currently it is not possible to use files with names like
        `names.csv'. Instead you have to use soft links or rename
        files. As an alternative one might use, for example a dbh
        attribute 'table_map'. It might be a hash ref, the keys
        being the table names and the values being the file names.

    Column name mapping
        Currently the module assumes that column names are stored in
        the first row. While this is fine in most cases, there
        should be a possibility of setting column names and column
        number from the programmer: For example MS Access doesn't
        export column names by default.

KNOWN BUGS
    *       The module is using flock() internally. However, this
            function is not available on platforms. Using flock() is
            disabled on MacOS and Windows 95: There's no locking at
            all (perhaps not so important on these operating
            systems, as they are for single users anyways).

AUTHOR AND COPYRIGHT
    This module is Copyright (C) 1998 by

        Jochen Wiedmann
        Am Eisteich 9
        72555 Metzingen
        Germany

        Email: joe@ispsoft.de
        Phone: +49 7123 14887

    All rights reserved.

    You may distribute this module under the terms of either the GNU
    General Public License or the Artistic License, as specified in
    the Perl README file.

SEE ALSO
    the DBI(3) manpage, the Text::CSV_XS(3) manpage, the
    SQL::Statement(3) manpage

    For help on the use of DBD::CSV, see the DBI users mailing list:

      http://www.isc.org/dbi-lists.html

    For general information on DBI see

      http://www.symbolstone.org/technology/perl/DBI