http://www.perlmonks.org?node_id=923645

edi has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks, How to check whether a MySQL database exist or not? 
use DBI;
eval { $dbh = DBI->do('dbi:mysql: xxxxx','root','')
 or die "Connection Error: $DBI::errstr\n"} ;



    if ($dbh == 'undef') {

           print "Table  does not exist.\n";
    }
    else {
        print "table exist";
    }

[download]
Thank you in advance!

Replies are listed 'Best First'.
Re: How to find MySQL database exist or not
by rcaputo (Chaplain) on Sep 01, 2011 at 17:46 UTC

    Query MySQL's internal tables for the information: 

    1) macbookpoe:~% mysql -BN -e 'select count(1) from information_schema
+.TABLES where TABLE_SCHEMA="test" and TABLE_NAME="moo"'

1

1) macbookpoe:~% mysql -BN -e 'select count(1) from information_schema
+.TABLES where TABLE_SCHEMA="test" and TABLE_NAME="moue"'

0

    [download]

    --
    Rocco Caputo - http://poe.perl.org/ - irc://irc.perl.org/poe

[reply]
[d/l]
Re: How to find MySQL database exist or not
by roboticus (Chancellor) on Sep 01, 2011 at 15:31 UTC

    edi:

    I'd make the following change:

    if (defined $dbh) { print "Table does not exist.\n"; }

    [download]

    The version you have checks whether $dbh is 0. (Had you used eq instead of ==, it would have checked whether $dbh contained the string 'undef'.)

    ...roboticus

    When your only tool is a hammer, all problems look like your thumb.

[reply]
[d/l]
      I would not make the same change. Why bother wrapping an "X or die" inside an eval, then check whether X is false afterwards? 
      if ($dbh = DBI->do('dbi:mysql: xxxxx','root','')) {
    print "Table exists\n"
} 
else {
    print "Table does not exists";
}

      [download]
      Of course, all it checks is whether one can connect - not whether a database exists (title question) or whether a table exists (message printed).
[reply]
[d/l]

        JavaFan:

        Good point. I just saw the $blah == 'undef' and was immediately horrified.

        ;^)

        ...roboticus

        When your only tool is a hammer, all problems look like your thumb.

[reply]
[d/l]
        And, once we are at nitpicking, it checks it after the program starts, not before (per spec). :)
[reply]
        thank you JavaFun for the reply. but it is giving an error as follows: Name "main::dbh" used only once: possible typo at C:/Program Files..... Can't locate auto/DBI/do.al in @INC
[reply]
       
use DBI;
eval { $dbh = DBI->do('dbi:mysql:xxxxxxx','root','')
 or die "Connection Error: $DBI::errstr\n"
} ;

if (defined $dbh) { print "Table does not exist.\n"; } 
else { print "Table exist";}

      [download]
      code will print "Table exist" whether the database exist or not. Please help.
[reply]
[d/l]
        I think that you are mixing up a couple of things.

        There is a dataset name ($dsn) which is a mySQL database on a particular host name and port number. That has to exist or you are going "nowhere"!

        If the $dsn exists, then you can attempt to connect to it. This is where the user name and passwords are required.

        my $dsn = "DBI:mysql:database=$database;host=$hostname;port=$port"
       || die "DB data set name failed $!\n";
#
# second step #
#
my $dbh = DBI->connect($dsn, $user, $password) 
                || die "DB connect failed $!\n";

        [download]
        The $dsn and the final connected handle, $dbh are very different things.

[reply]
[d/l]
Re: How to find MySQL database exist or not
by Corion (Patriarch) on Sep 02, 2011 at 12:50 UTC

    Have a look at the Catalog Methods of DBI. With these, you can easily find out what databases, tables and columns exist.

[reply]
Re: How to find MySQL database exist or not
by Anonymous Monk on Sep 02, 2011 at 11:41 UTC
[reply]

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