Re: if (empty record set)

Using $sth->rows() is the answer if you need to actually work with the data, but if you just need to see if there are rows that match, consider using: (untested)

my $SQLString "select COUNT(1) from there";
$sth = $dbh->prepare($SQLString);
$sth->execute();
@bkmark = $sth->fetchrow;
if($bkmark[0] == 0)
{
  ...........
}
[download]

Comment on Re: if (empty record set) Select or Download Code

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Re: Re: if (empty record set) by CountZero (Bishop) on Jun 26, 2003 at 16:13 UTC
If you are working with mySQL `SELECT COUNT () FROM ...` is particularly fast, the engine being optimised for such things. So if you just want to know if there are any records available, thats the way to do it, rather than fetching the records themselves. If you need the data also, of course it is better to go with the other suggestions. CountZero "If you have four groups working on a compiler, you'll get a 4-pass compiler."* - Conway's Law	[reply] [d/l]
Re: Re: if (empty record set) by Grygonos (Chaplain) on Jun 26, 2003 at 15:10 UTC
on many RDBMS the execute method will return the number of rows like so: `my $query = "SELECT * FROM myTable"; $sth = $dbh->prepare($query); if(!$sth->execute()) { ... }` [download] it varies from system to system .. but is another way to accomplish what you want edit: you could also run this query `SELECT Count(yourPrimaryKeyHere) FROM yourTable` if you're on a database that doesn't support execute's return value or `$sth->rows`	[reply] [d/l] [select]
Re: Re: Re: if (empty record set) by Lachesis (Friar) on Jun 26, 2003 at 15:35 UTC
Thats not the way execute works in DBI. Check the docs, but to summarise for you now If an error occurs you get undef back If it doesn't know the number of rows affected get -1 back If no rows are affected you will get 0E0 back. otherwise you get the number of rows affected	[reply]
Re: Re: Re: Re: if (empty record set) by Grygonos (Chaplain) on Jun 26, 2003 at 16:24 UTC
The last time I tried it on MySQL it worked like that... but that was a while ago things may have changed... hope my old company doesn't upgrade their DBI because I used that return value from execute on a number of scripts which worked fine under that version of dbi... Thanks for the update.	[reply]


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