我如何知道Perl DBI查询返回多少行？

#!/usr/bin/perl
use strict;
use DBI;

# 数据库连接信息
my $dsn = "DBI:mysql:database=test;host=localhost";
my $username = "username";
my $password = "password";

# 连接数据库
my $dbh = DBI->connect($dsn, $username, $password, { RaiseError => 1 });

# 准备SQL查询
my $sth = $dbh->prepare("SELECT * FROM table_name");

# 执行查询
$sth->execute();

# 计算查询结果的行数
my $rows = 0;
while (my @row = $sth->fetchrow_array()) {
    $rows++;
}

# 输出结果
print "查询返回了 $rows 行\n";

# 关闭数据库连接
$sth->finish();
$dbh->disconnect();

#!/usr/bin/perl
use strict;
use DBI;

# 数据库连接信息
my $dsn = "DBI:mysql:database=test;host=localhost";
my $username = "username";
my $password = "password";

# 连接数据库
my $dbh = DBI->connect($dsn, $username, $password, { RaiseError => 1 });

# 准备SQL查询
my $sth = $dbh->prepare("SELECT COUNT(*) FROM table_name");

# 执行查询
$sth->execute();

# 获取查询结果的总行数
my ($rows) = $sth->selectrow_array();

# 输出结果
print "查询返回了 $rows 行\n";

# 关闭数据库连接
$sth->finish();
$dbh->disconnect();