检查数据库中是否存在数据

Question

What is the right way of checking if the required data is in the database?

What I use currently is,

mysql_query("SELECT anyfield FROM table WHERE field='$data'");

and then check the if any rows are affected.

But I dont really have any use with the extracted data anyfield . Eventhough the resource usage is so minor here, what is the right way to check if data exists in a db without extracting any other fields from the table?

Answer 1

Let the database count and retrieve the count data from the query.

$result = mysql_query('SELECT COUNT(*) FROM `table` WHERE `field` = ...');
if (!$result) {
    die(mysql_error());
}
if (mysql_result($result, 0, 0) > 0) {
    // some data matched
} else {
    // no data matched
}

Answer 2

$result = mysql_query("SELECT `field` FROM `table` WHERE `field` = '".$data."'");
if (mysql_num_rows($result)){
    // Rows exist
}

OR

$result = mysql_query("SELECT COUNT(`field`) as count FROM `table` WHERE `field` = '".$data."'");
$row = mysql_fetch_array($result);
if ($row ['count']){
    // Rows exist
}

Answer 3

I would ensure, if I was checking for data, that as little data was returned as possible.

Fetch one field (I usually do id ) and ensure you use LIMIT , eg. LIMIT 1 ... assuming you only want to know if any record exists.

Because you're using a PHP variable to find a record, if it suits your situation, you could perhaps do a LEFT JOIN on the first SQL line that gets $data , but that might just as easily be overkill for what you need.