问SQL INSERT SQL语句

EN

<?php
require "conn.php";
$UserID = $_POST["UserID"];
$EventID = $_POST["EventID"];

$query = "INSERT INTO Interested (UserID, EventID) 
SELECT '$UserID' , '$EventID' FROM Interested 
WHERE NOT EXISTS (SELECT UserID, EventID FROM Interested WHERE UserID = '$UserID' 
AND EventID = '$EventID') LIMIT 1;";

$result = mysqli_query($conn ,$query);
if(mysqli_num_rows($result) > 0)
{
    echo "Interested";
}
else
{
    echo "Duplicate";
}
?>

08-24 21:57:39.517 8553-9030/com.example.feelingoodlivinbeta.socialdreams_a1 E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #3
   Process: com.example.feelingoodlivinbeta.socialdreams_a1, PID: 8553
   java.lang.RuntimeException: An error occurred while executing doInBackground()
       at android.os.AsyncTask$3.done(AsyncTask.java:309)
       at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
       at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
       at java.util.concurrent.FutureTask.run(FutureTask.java:242)
       at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
       at java.lang.Thread.run(Thread.java:818)
    Caused by: java.lang.ArrayIndexOutOfBoundsException: length=2; index=2
       at com.example.feelingoodlivinbeta.socialdreams_a1.InterestedFunction.doInBackground(InterestedFunction.java:32)
       at com.example.feelingoodlivinbeta.socialdreams_a1.InterestedFunction.doInBackground(InterestedFunction.java:24)
       at android.os.AsyncTask$2.call(AsyncTask.java:295)
       at java.util.concurrent.FutureTask.run(FutureTask.java:237)
       at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234) 
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 
       at java.lang.Thread.run(Thread.java:818)