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' => 'csv'};
       $sth = $dbh->prepare("SELECT * FROM info");

       # Read /etc/passwd as a CSV file.

WARNING
   THIS IS ALPHA SOFTWARE. It is *only* 'Alpha' because the interface (API)
   is not finalised. 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 Acess 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, 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 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
   (aka files). It defaults to the current directory, thus the following
   are equivalent:

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

   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 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 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 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::File,
   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::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

   Additional 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. Altrenatively 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 meta data. 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".
       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.

 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.

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

   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.

   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:
           There's no locking at all (perhaps not so important on MacOS, as
           there's a single user anyways).

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

       Jochen Wiedmann
       Am Eisteich 9
       72555 Metzingen
       Germany

       Email: [email protected]
       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

   A mailing list for supporting the DBD::CSV driver is available at

     http://mail.healthquiz.com/mailman/listinfo/dbd-csv

   For general information on DBI see

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

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