在插入之前检查值，如果已经存在，请不要使用 php 在 mysql 上插入它

Question

I have code check ips addresses if duplicated will redirected to another link but the code is running good when insert value in ( ip,user_agent,time ) in table ( click ) first time but when i try to check if running with some value it written again on database I need any value ( ip,user_agent,time ) write just one time after written to database not written the some value ( ip,user_agent,time )

<?php
    $servername = "localhost";
    $username = "root";
    $password = "rootroot";
    $dbname = "data_clicks";
    //Create connection to database using mysqli
    $conn = new mysqli($servername, $username , $password, $dbname);



    //Set variables according to user input on previous form
    if(isset($_SERVER['REMOTE_ADDR']) && isset($_SERVER['HTTP_USER_AGENT'])){
        $ip = $_SERVER['REMOTE_ADDR'];
        $user = $_SERVER['HTTP_USER_AGENT'];
        $datetime = date_create()->format('d-m-Y ');
    }


    //Define the INSERT statement with IGNORE keyword
        $sql = "INSERT IGNORE INTO clicks (ip, user_agent, time )
        VALUES ('.$ip.', '.$user.', CURRENT_TIMESTAMP)";
        if ($conn->query($sql) === false) {
            die("Database error:".$conn->error);
        }
    // link offer
    $file = "md5.txt";
    $f = fopen($file, 'r');
    $line = fgets($f);
    fclose($f);
    $link="https://facebook.com/?".$line;
    //do smth

    $contents = file($file, FILE_IGNORE_NEW_LINES);
    $first_line = array_shift($contents);
    file_put_contents($file, implode("\r\n", $contents));

    // Check for success
        if ($conn->affected_rows == 0) {
            print "<br>Error! <p></p>";
            echo "" . $ip .''.$user. " already exists in the DCR";
            header("Location: http://www.google.com/");
        } else {

    //Success and return new id
            echo "<br><p></p>Record Added!<p></p>";
            header("Location: $link");
        }
    ?> 

Answer 1

I have code check ips addresses if duplicated will redirected to another link but the code is running good when insert value in ( ip,user_agent,time ) in table ( click ) first time but when i try to check if running with some value it written again on database I need any value ( ip,user_agent,time ) write just one time after written to database not written the some value ( ip,user_agent,time )

<?php
    $servername = "localhost";
    $username = "root";
    $password = "rootroot";
    $dbname = "data_clicks";
    //Create connection to database using mysqli
    $conn = new mysqli($servername, $username , $password, $dbname);



    //Set variables according to user input on previous form
    if(isset($_SERVER['REMOTE_ADDR']) && isset($_SERVER['HTTP_USER_AGENT'])){
        $ip = $_SERVER['REMOTE_ADDR'];
        $user = $_SERVER['HTTP_USER_AGENT'];
        $datetime = date_create()->format('d-m-Y ');
    }


    //Define the INSERT statement with IGNORE keyword
        $sql = "INSERT IGNORE INTO clicks (ip, user_agent, time )
        VALUES ('.$ip.', '.$user.', CURRENT_TIMESTAMP)";
        if ($conn->query($sql) === false) {
            die("Database error:".$conn->error);
        }
    // link offer
    $file = "md5.txt";
    $f = fopen($file, 'r');
    $line = fgets($f);
    fclose($f);
    $link="https://facebook.com/?".$line;
    //do smth

    $contents = file($file, FILE_IGNORE_NEW_LINES);
    $first_line = array_shift($contents);
    file_put_contents($file, implode("\r\n", $contents));

    // Check for success
        if ($conn->affected_rows == 0) {
            print "<br>Error! <p></p>";
            echo "" . $ip .''.$user. " already exists in the DCR";
            header("Location: http://www.google.com/");
        } else {

    //Success and return new id
            echo "<br><p></p>Record Added!<p></p>";
            header("Location: $link");
        }
    ?>