perl, testing a database for a match

Shell Programming and Scripting
1

hi there.

in perl, I am struggling to find a simple method of connecting to a database, determining if the result of my query is "true" and then testing against the result. I dont even really want the data that i am 'SELECT'�ng. i effectively just want to check that a record exists with a UID column (primary key) that exactly matches the $uid that has been passed to my script.

I have managed to fudge a solution together that involves me having to

NOTE: the $uid is passed to script as an argument to the script

1) going to the db and doing "SELECT UID FROM table WHERE UID = $uid"

2) using fetchall_arrayref() to pull the result into an array (although should never be more than one return seeing as the data being requested is a primary key)

3) cycling through the array and sending each value to a fine in /tmp

seeing as this file will only ever contain something or nothing, i do a test later on the script to see if the file has content, if it does, i know that my query was "true" so to speak and I can be sure this a record for the $uid passed to my script in the database

I know that this seems a ridiculously over the top way to do this, but i am relatively new to perl and it was the only way i could get it to work.

# this value will in reality be passed to this script via a getopts cli argument
my $uid = '1234'     #as an example

my $dbh = DBI->connect("DBI:mysql:DB1","user","pass",) or die $DBI::errstr;
my $sth = $dbh->prepare("SELECT UID FROM table WHERE UID = $uid") or die $DBI::errstr;
       
 $sth->execute or die $DBI::errstr;
        
my $finalref = $sth->fetchall_arrayref();


        
foreach (@$finalref) {
      system("echo @$_ >> /tmp/results");
}

I just wondered if any of the fine gurus on this site could advise me a way of doing a simple 1/2 line version of the above without all the faffing about that ive had to do :). bear in mind, all i need to do is test that a record exists, i dont even need to pull any data from the DB or send any to it at this stage

any help on this would be greatly appreciated

2

After selecting the data you could build your logic using:

$sth->rows

You don't need to fetch any data.

P.S. You don't even need real data in the select list:

select null from table where ...

and then:

$sth->rows and continue here ... or just stop.

No rows will be evaluated as false in boolean context.

3 
my $uid = '1234'     #as an example

my $db = DBI->connect("DBI:mysql:DB1","user","pass",) or die $DBI::errstr;
my $sql= qq~SELECT UID FROM table WHERE UID = $uid~; 

my $rv = $db->selectcol_arrayref( $sql )->[0];

$rv ? print "We Have UID $rv\n" : print "No UID $rv found\n";