Prevent multiple data entries in MySQL

So here is the deal. I have looked around everywhere, and all other techniques relate to refreshing the browser, and methods to prevent the php page from resubmitting the post data. I am new to this (obviously :p) But anyways, my questions I believe is simple. I just want a method, possibly an if else statement that would check the post data entries, and if there is a match already in my table, than do not execute the query. I am not worried about querying all of the results of the table, as I only suspect this table will ever have 50-60 entries.

Here is the php page that handles the form submission:

$firstName = $_POST['firstName'];
$lastName = $_POST['lastName'];
$email = $_POST['email'];
$city = $_POST['city'];
$state = $_POST['state'];

$submitDate = date("Y-m-d");

mysql_connect ("localhost", "abc", "123") or die ('Error: ' . mysql_error());
mysql_select_db ("members");

$query = "INSERT INTO persons (ID, firstName, lastName, email, city, state, submitDate)VALUES (
'NULL',
'".$firstName."',
'".$lastName."',
'".$email."',
'".$city."',
'".$state."',
'".$submitDate."'
)";

mysql_query($query) or die ('Error Updating database');

echo "Database Updated With: " .$firstName ." " .$lastName ." " .$email ." " .$city ." " .$state; 

mysql_close($con);

Sorry, cant ever seem to get my php to format correctly with those code braces. Anyways. just to re-iterate, looking for a way to maybe based on the first and last name. if those already exist, then do not allow the submission of the data. I have tried a few if then statements but i do not think I am getting the concept down of comparing the result to my query. I hope this all makes sense!!!

---

您可以使用INSERT IGNORE INTO ...并让MySQL处理它。

$query = "INSERT IGNORE INTO persons (ID, firstName, lastName, email, city, state, submitDate) VALUES (
'NULL',
'".$firstName."',
'".$lastName."',
'".$email."',
'".$city."',
'".$state."',
'".$submitDate."'
)";

---

我会建议在你想要唯一的列上添加一个UNIQUE索引。

---

I had this issue as well. Basically what I did is before the insert, do a select on the criteria that would qualify as a duplicate and check for it to return; if it does not we are ok to enter.

$query = "SELECT COUNT(id) AS mycount FROM persons WHERE firstName = '".$firstnName."' AND lastName = '".$lastName."'";
$result = mysql_query($query);
$row = mysql_fetch_array($result);
if($row['mycount'] == 0) {
    //Do insert
}

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