how to test for empty result set

Anon

Hi all -

What is the best way to test the result set of a query for emptiness.

The situation is basically this:

I want to add a record to a MySQL table. I want to check if a record exists for a given id #.

I set up a statement which says:

if the result of a query is empty, the id # doesn't exist, therefore do something to add a new record.

if the result of the query is not empty, the id # does exist so do something else to add a new record.

I'm having trouble testing whether the result of the query is empty so I can't set up the decision structure properly.

I'd appreciate advice on how to approach the situation. If this is not a clear enough explanation I can flesh out the details to give more context.

Thanks,

Kris

Anon

$sql = "select * from $table";
$result = mysql_query($sql, $conn);
$number = mysql_num_rows($result);
if($number > 0){...}
else{...}

Anon

$sql = "select from $table";
$result = mysql_query($sql, $conn);
if($myrow = $mysql_fetch_array($result)){...}
else{ / No rows were found, bo-hoo! */ }

Anon

$query = "SELECT * FROM Users";
$results = mysql_query($query);

if (mysql_num_rows($results) == 0) {

echo "No Users Found";

}

Anon

if the result of a query is empty, the id # doesn't exist, therefore
do something to add a new record.

Aren't you setting up a race condition here? Multiple clients can
all attempt the same thing simultaneously, meaning that two or
more could search for the ID and not find it, and so perform
conflicting inserts. But if you attempt the insert first (assuming
a properly designed database where the ID is defined as unique)
then the race condition is absent.