sql server对exists检查查询的精度无效

use DBI;
$idx = '12345';
$query = 'if exists (select * from tbl where idx = ?) select top 10 * from tbl';
my $h = $dbh->prepare($query) or die "Couldn't prepare query: " . $dbh->errstr;
$h->execute($idx) or die "Couldn't execute statement: " . $h->errstr;

但是请注意,如果我尝试使用此方法

use DBI;
$query = 'if exists (select * from tbl where idx = \'12345\') select top 10 * from tbl';
my $h = $dbh->prepare($query) or die "Couldn't prepare query: " . $dbh->errstr;
$h->execute() or die "Couldn't execute statement: " . $h->errstr;

那就行了。我真的很困惑怎么了?在查询中,可能导致无效的精度错误。

谢谢任何人能提供的帮助。