Check whether records exist in database - php

Question

I know there are various offered solutions for this topic posted on this site, and I checked (and used) some of those solutions. Nevertheless, I can't figure out why my code below does not work, probably because I'm a starter with respect to php and sql programming ;-(
The code is supposed to add a record with 3 fields (FirstName, LastName, Age) in a table (persons), but only if the record does not already exist. Therefore a check on existing FirstName and Lastname fields is performed. But in case of existing record the condition of the if statement still seems to be true and a copy of the existing record is still inserted into the database. What do I miss?
Thanks in advance for the help.
//check whether item does not exist in database
$query ="SELECT FirstName,LastName FROM persons
WHERE FirstName='$data[1]' AND LastName='$data[2]'";
$result = mysql_query($query);
if($result && mysql_num_rows($result) > 0)
{
echo " <br> record exist";
}
else
{
$theage = (int)$data[3]; //! for conversion of integer values
$sql="INSERT INTO persons (FirstName, LastName, Age)
VALUES ('$data[1]','$data[2]','$theage')";
if (!mysqli_query($con,$sql))
{
die('Error: ' . mysqli_error($con));
}
}

Answer 1

You have to use {} around array values in query
$query ="SELECT FirstName,LastName FROM persons
WHERE FirstName='{$data[1]}' AND LastName='{$data[2]}'";
Also your INSERT query runs on mysqli and SELECT query runs on mysql. You have to use only 1 not both and use below code with mysqli.
$result = mysqli_query($con,$query);
if($result && mysqli_num_rows($result) > 0)
{
echo " <br> record exist";
}

Answer 2

May be this query will help you:
INSERT INTO persons (FirstName, LastName, Age)
SELECT * FROM (SELECT FirstName,LastName) AS tmp
WHERE NOT EXISTS (
SELECT FirstName, LastName FROM persons WHERE WHERE FirstName='$data[1]' AND LastName='$data[2]'
) LIMIT 1;

Answer 3

Check your connection
In first query you have used
mysql_query
then in second case at the time of insert you use
mysqli_query

Answer 4

From the database perspective, modify your Person table design by setting a UNIQUE KEY for the necessary fields i.e :
CREATE TABLE `Persons` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`FirstName` varchar(255) NOT NULL,
`LastName` varchar(255) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `unique_FirstName_LastName` (`FirstName`,`LastName`) USING BTREE
)ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=latin1;
Do a normal insert, handle the duplicate error
[Err] 1062 - Duplicate entry 'jk-kenneth' for key 'unique_FirstName_LastName'