Conditional PDO bindParam Update - php

Question

So I'm trying to do a conditional update but I seem to be having problems with binding the data with the statement.
function:
function updateEditor($email, $first, $last, $id){
global $DBH;
$response = false;
$upemail = "";
$upfirst = "";
$uplast = "";
$stmt = "SELECT memEmail, memFirst, memLast FROM MEMBER WHERE memID = :id";
try{
$STH = $DBH->prepare($stmt);
$STH->bindParam(':id', $id);
$STH->execute();
$STH->setFetchMode(PDO::FETCH_ASSOC);
$row = $STH->fetch();
if($row['memEmail'] != $email){ $upemail = $email;}
if($row['memFirst'] != $first){ $upfirst = $first;}
if($row['memLast'] != $last){ $uplast = $last;}
}catch(PDOException $e) {
echo $e->getMessage() . "first";
}
$stmt .= "UPDATE MEMBER SET ";
if(!empty($upemail)){
$stmt .= "memEmail = :memEmail";
if(!empty($upfirst) || !empty($uplast)){
$stmt .= ", ";
}
}
if(!empty($upfirst)){
$stmt .= "memFirst = :memFirst";
if(!empty($uplast)){
$stmt .= ", ";
}
}
if(!empty($uplast)){
$stmt .= "memLast = :memLast";
}
if(empty($upemail) && empty($upfirst) && empty($uplast)){
return false;
}else{
$stmt .= " WHERE memID = :id";
}
try{
$STH = $DBH->prepare($stmt);
if(!empty($upemail)){$STH->bindParam(':memEmail', $upemail);}else{$STH->bindParam(':memEmail', $row['memEmail']);}
if(!empty($upfirst)){$STH->bindParam(':memFirst', $upfirst);}else{$STH->bindParam(':memFirst', $row['memFirst']);}
if(!empty($uplast)){$STH->bindParam(':memLast', $uplast);}else{$STH->bindParam(':memLast', $row['memLast']);}
$STH->bindParam(':id', $id);
$STH->execute();
$STH->setFetchMode(PDO::FETCH_ASSOC);
$response = true;
}catch(PDOException $e) {
echo $e->getMessage() . "second";
$response = $e->getMessage() . "second";
}
return $response;
}
I have tried putting the variables into the statement, using ?, and the code above so far. The error I keep getting is:
SQLSTATE[HY093]: Invalid parameter number: number of bound variables does not match number of tokens

Answer 1

Here:
$stmt .= "UPDATE MEMBER SET ";
you append the UPDATE to the previous $stmt string. You'll end up with:
$stmt = "SELECT memEmail, memFirst, memLast FROM MEMBER WHERE memID = :idUPDATE MEMBER SET "; // and the rest
reulting in one identifier more (:idUPDATE).
Remove the . to start a new query in this string.
$stmt = "UPDATE MEMBER SET ";
Note:
You are making this way too complicated. Skip the checks for empty values, just update all columns when you update a dataset, you don't gain anything by checking what has changed and what hasn't first.

Answer 2

Besides #Gerald Schneider answer, you are setting the param in both cases (if/else)
if(!empty($upemail)){$STH->bindParam(':memEmail', $upemail);}else{$STH->bindParam(':memEmail', $row['memEmail']);}
But are defining the parameters only in one case
if(!empty($upemail)){
$stmt .= "memEmail = :memEmail";
if(!empty($upfirst) || !empty($uplast)){
$stmt .= ", ";
}
}
if(!empty($upfirst)){
$stmt .= "memFirst = :memFirst";
if(!empty($uplast)){
$stmt .= ", ";
}
}
if(!empty($uplast)){
$stmt .= "memLast = :memLast";
}
There's no else condition