Comparing if values exist in database

Question

I am having trouble as to why the statement below won't do as I expect. Below is just a snippet and i am trying to compare the two post variables to the database table...

   if ($_SERVER['REQUEST_METHOD'] == 'POST'){
       $user_databaseF = $_POST['firstname_'] ;
       $user_databaseS = $_POST['lastname_'];
       $table_check_query = "SELECT * FROM clients_table WHERE _first = '$user_databaseF' AND _surname = '$user_databaseS'";
       $result_of_table_query =  $mysqli->query($table_check_query);
    if(empty($result_of_table_query)) {
       echo " we are good to start" ;    // Im getting duplicates in table

I'm thinking its here if(empty($result_of_table_query))

weird... im assuming the results are always empty... dont know why — Careen
– Careen, Commented May 2, 2015 at 18:55

u_mulder · Accepted Answer · 2015-05-02 18:57:16Z

empty function checks if variable is empty. But mysqli::query returns either a boolean true/false, or a mysqli_result object.

Your comparison empty($result_of_table_query) will be true only if mysqli::query return false. This will happen in case of query error. Empty result is not an error. I advise you to do this:

 $table_check_query = "SELECT count(*) as `count` FROM clients_table WHERE _first = '$user_databaseF' AND _surname = '$user_databaseS'";
 $db_result =  $mysqli->query($table_check_query);
 // as a result of a query you will have a mysqli_result object
 // to get values in a result use for example `fetch_array`
 $result = $db_result->fetch_array();
 // print_r $result to check what you have.
 // if all is cool there will be an array with key `count`
 // which will contain number of records. Check it:
 if ($result['count'] == 0) { /* you have no duplicates */ }

Mureinik · Accepted Answer · 2015-05-02 18:59:57Z

1

empty returns TRUE for a value that is empty or evaluates as FALSE. An empty mysqli_result is neither.

Instead, you can use mysqli_num_rows to check how many results the query returns:

$result_of_table_query =  $mysqli->query($table_check_query);
if(mysqli_num_rows($result_of_table_query) == 0) {
    echo "we are good to start";

answered May 2, 2015 at 18:59

Mureinik

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