Question

I have the following code :

sub run_query { 
    my $name = shift || undef;
    my $sql  = (defined $name ) ? "select * from table where name = ?" :
                                  "select * from table";
    my $sth  = $dbh->prepare("$sql");
    $sth->execute($name);
}

The above subroutine need to work as follows: if $name is provided, then run the first query, else fetch all the data from the table. How can I bind the name field? I’d like it bound dynamically if it is provided.

Answer 1

From the DBI documentation on cpan:

A common issue is to have a code fragment handle a value that could be
either defined or undef (non-NULL or NULL) at runtime. A simple
technique is to prepare the appropriate statement as needed, and
substitute the placeholder for non-NULL cases:

  $sql_clause = defined $age ? "age = ?" : "age IS NULL";
  $sth = $dbh->prepare(qq{
    SELECT fullname FROM people WHERE $sql_clause
  });
  $sth->execute(defined $age ? $age : ());

It does not exactly apply to your question, which I assume is that your execute fails if you add an argument where one is not expected. So, the last line here would apply:

  $sth->execute(defined $name ? $name : ());