NAME
    DBD::CSV - DBI driver for CSV files

SYNOPSIS
        use DBI;
        $dbh = DBI->connect("DBI:CSV:directory=/home/joe/csvdb")
            or die "Cannot connect: " . $DBI::errstr;
        $sth = DBI->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();

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 implements access to so-called CSV
    files (Comma separated values). Such files are mostly used for
    exporting MS Acess and MS Excel data.

    See the DBI(3) manpage for details on DBI and the
    SQL::Statement(3) manpage for details on SQL::Statement.

  Prerequisites

    The only system dependent feature that DBD::CSV 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, on Windows 95 and NT.

    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 0.93
        or a later release

    Text::CSV_XS
        this module is used for writing rows to or reading rows from
        CSV files. Note that you need version 0.10, the C version
        and not the old Perl- only version.

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

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

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

    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");

    The table is created as an empty file, then a first row with
    column names will be written into the file. 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 table names to be 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 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 they don't contain binary
    data.

    Next an example using parameters:

        $dbh->do("INSERT INTO $table VALUES (?, ?)",
                 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. See the section on "Data
    restrictions" below for possible problems.

    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
    section on "Data restrictions" below for possible problems. 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");

  Data restrictions

    When inserting and fetching data, you will sometimes be
    surprised: DBD::CSV doesn't correctly handle data types, in
    particular NULL's. 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.

  Error handling

    In the above examples we have never cared for 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::CSV, thus they all work like expected:

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

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

    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.

        See the section on "Data restrictions" above for details.

    These attributes and methods are not supported:

        bind_param_inout
        CursorName
        LongReadLen
        LongTruncOk

    Additional to the DBI attributes, you can use the following:

    directory
        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.

    eol
    quote_char
    escape_char
    sep_char
        These are corresponding to the same attributes of the
        Text::CSV_XS object.

        You need access to the DBD::CSV_XS object, if you want to
        work with non-default CSV files. For example, the following
        will advice the DBD::CSV_XS file to use semicolons as field
        separators:

            $dbh->{'sep_char'} = ';';

        Note that DBD::CSV will put the Text::CSV_XS object into
        binary mode, so that you can safely work with arbitrary
        data. You must not change this!

  Driver private methods

    data_sources
        The `data_sources' method returns a list of subdirectories
        of the current directory in the form
        "DBI:CSV:directory=$dirname". Unfortunately the current
        version of DBI doesn't accept attributes of the data_sources
        method. Thus the method reads a global variable

            $DBD::CSV::dr::data_sources_attr

        if you want to read the subdirectories of another directory.
        Example:

            my($drh) = DBI->install_driver("CSV");
            $DBD::CSV::dr::data_sources_attr = "/usr/local/csv_data";
            my(@list) = $drh->data_sources();

    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.

TODO
    Joins
        The current version of the module works with single table
        SELECT's only, although the basic design of the
        SQL::Statement module allows joins and the likes.

    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.

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

