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SQL Anywhere 10.0.1 » SQL Anywhere Server - Programming » SQL Anywhere Perl DBD::SQLAnywhere API » Writing Perl scripts that use DBD::SQLAnywhere

Opening and closing a connection Next Page

Selecting data


Once you have obtained a handle to an open connection, you can access and modify data stored in the database. Perhaps the simplest operation is to retrieve some rows and print them out.

SQL statements that return row sets must be prepared before being executed. The prepare method returns a handle to the statement. You use the handle to execute the statement, then retrieve meta information about the result set and the rows of the result set.

#!/usr/local/bin/perl -w
#
use DBI;
use strict;
my $database = "demo";
my $data_src = "DBI:SQLAnywhere:ENG=$database;DBN=$database";
my $uid      = "DBA";
my $pwd      = "sql";
my $sel_stmt = "SELECT ID, GivenName, Surname
                FROM Customers
                ORDER BY GivenName, Surname"; 
my %defaults = (
     AutoCommit => 0, # Require explicit commit or rollback.
     PrintError => 0
   );
my $dbh = DBI->connect($data_src, $uid, $pwd, \%defaults)
  or die "Can't connect to $data_src: $DBI::errstr\n";
&db_query($sel_stmt, $dbh);
$dbh->rollback;
$dbh->disconnect;
exit(0);

sub db_query {
      my($sel, $dbh) = @_;
      my($row, $sth) = undef;
      $sth = $dbh->prepare($sel);
      $sth->execute;
      print "Fields:     $sth->{NUM_OF_FIELDS}\n";
      print "Params:     $sth->{NUM_OF_PARAMS}\n\n";
      print join("\t\t", @{$sth->{NAME}}), "\n\n";
      while($row = $sth->fetchrow_arrayref) {
         print join("\t\t", @$row), "\n";
      }
      $sth = undef;
}
__END__

Prepared statements are not dropped from the database server until the Perl statement handle is destroyed. To destroy a statement handle, reuse the variable or set it to undef. Calling the finish method does not drop the handle. In fact, the finish method should not be called, except when you have decided not to finish reading a result set.

To detect handle leaks, the SQL Anywhere database server limits the number of cursors and prepared statements permitted to a maximum of 50 per connection by default. The resource governor automatically generates an error if these limits are exceeded. If you get this error, check for undestroyed statement handles. Use prepare_cached sparingly, as the statement handles are not destroyed.

If necessary, you can alter these limits by setting the max_cursor_count and max_statement_count options. See max_cursor_count option [database], and max_statement_count option [database]