CODEWITHSUNDEEP
mysqlperldbi
James Brown
James Brown

Reputation: 919

How to check for an empty set when using Perl DBI->MySQL

Is there a way to check if a DBI->execute statement returns an empty set? The purpose is that I want to create a table, and then ask for username, if the username isn't in the table, (check for empty fetch() statement), then add to table. Any suggestions?

    $sth = $dbh->prepare("SELECT * FROM table_name_here");
    $sth->execute();

    if(...$sth->fetch() was empty...)
    do something...

Upvotes: 1

Views: 5506

Answers (4)

Borodin
Borodin

Reputation: 126722

I suggest you do a preliminary fetch of the number of records, like this

my ($records) = $dbh->selectrow_array('SELECT count(*) FROM table_name_here');

Upvotes: 2

Galimov Albert
Galimov Albert

Reputation: 7357

Is there a way to check if a DBI->execute statement returns an empty set

Yes.

$sth = $dbh->prepare("SELECT * FROM table_name_here");
$sth->execute();
unless( $sth->rows ) {
    #empty set
}

Upvotes: 2

raina77ow
raina77ow

Reputation: 106385

One possible approach to do that:

my $row_count = 0;
while (my @ary = $sth->fetchrow_array() ) { ...; $row_count++; }
unless ($row_count) { 
  ...
}

But I can't help wondering why do you need to use fetchrow, and not fetchall, for this specific case. In fact, I'd reorganize it this way:

my ($count) = $dbh->selectrow_array('
   SELECT COUNT(*) FROM users WHERE username = ?'
   undef, $username);
if ($count) { ... }

Upvotes: 1

Gilles Quénot
Gilles Quénot

Reputation: 185053

Try that :

$sth = $dbh->prepare("SELECT * FROM table_name_here");
$sth->execute();

unless ($sth->fetch()) { do something..; }

Upvotes: 2

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