PDO MYSQL Update Only If Different - php

Question

I have a web program which allows the administrator to update a user's information... With that being said, I only want columns updated which have indeed been 'updated'...
I have done quite a bit of researching on this and it seems that all methods use outdated querys, which do not make use of the prepare statement to escape input...
Can someone please help me with the statement?
Essentially in psuedocode:
Update FIRSTNAME if $editedUserdata['firstname'] != FIRSTNAME, LASTNAME if $editedUserData['lastname'] != LASTNAME ...etc...
Here is what I have for the post code...
$password = sha1($password);
$editedUserData = array(
'firstname' => $firstname,
'lastname' => $lastname,
'username' => $username,
'password' => $password,
'cellphone' => $cellphone,
'security_level' => $seclvl,
'email' => $email,
'direct_phone' => $direct,
'ext_num' => $extension,
'is_active' => $userflag
);
Then it should be something like
$query = $this->db->prepare('UPDATE FIRSTNAME if(?) IS NOT FIRSTNAME, LASTNAME if(?) IS NOT LASTNAME, USERNAME if (?) IS NOT USERNAME.... VALUES (:firstname, :lastname, :username).....'
if ($query -> execute($editedUserData)) {
more code....

Answer 1

According to MySQL documentation -
Ref: (http://dev.mysql.com/doc/refman/5.0/en/update.html)
"If you set a column to the value it currently has,
MySQL notices this and does not update it."

Answer 2

Maybe I'm not understanding the problem which you're trying to solve but you don't have to test if field value did change.
If field value is "A" and you put there an "A" it will remain the same otherwise, if you put there a "B" it will be updated as expected
The prepared statement would be something like
$stmt = $dbh->prepare("
UPDATE table_name
SET
field1 = :value1,
field2 = :value2
WHERE
field0 = :key
");
$stmt->bindParam(':value1', $value1, PDO::PARAM_STR);
$stmt->bindParam(':value2', $value2, PDO::PARAM_STR);
$stmt->bindParam(':key', $key, PDO::PARAM_INT);
$stmt->execute()

Answer 3

Run a single statement to update the row.
Firstly, what's the unique identifier for a row in the users table, is there a unique userid or username? You'll want a WHERE clause on the UPDATE statement so that only that row will be updated.
The normative pattern for an UPDATE statement to update several columns in a single row is like this:
UPDATE users
SET col2 = 'value'
, col3 = 'another value'
, col4 = 'fi'
WHERE idcol = idvalue ;
To use a prepared statement with PDO, the SQL text could look something like this, if you use named placeholders:
UPDATE users
SET col2 = :col2_value
, col3 = :col3_value
, col4 = :col4_value
WHERE idcol = :id_value
Or this, if you use positional notation for the placeholders:
UPDATE users
SET col2 = ?
, col3 = ?
, col4 = ?
WHERE idcol = ?
(My personal preference is to use the named placeholders, rather than positional, but either will work.)
This is how I'd do it, run the prepare, then the bind_param, and then the execute.
$sql = "UPDATE users
SET col2 = :col2_value
, col3 = :col3_value
, col4 = :col4_value
WHERE idcol = :id_value ";
$stmt = $dbh->prepare($sql);
$stmt->bindParam(':col2_value', $col2_val, PDO::PARAM_STR);
$stmt->bindParam(':col3_value', $col3_val, PDO::PARAM_STR);
$stmt->bindParam(':col4_value', $col4_val, PDO::PARAM_STR);
$stmt->bindParam(':id_value' , $id_val, PDO::PARAM_STR);
$stmt->execute();
To do something different, to dynamically create the SQL text, and adjust the bindParam calls, that would add unnecessary complexity to the code. There's no performance advantage to doing that; when that UPDATE statement runs, MySQL has to lock the row, store a new copy of the row. It doesn't really save anything (aside from a few bytes of data transfer) to avoid sending a column value that hasn't changed.

Answer 4

If you realy want to use cases, read this.
There is no reason to do it in your case, as stated from #spencer7593 in the comments:
That's WAY more overhead... roundtrips to the database, parsing the
statement, developing an execution plan, executing the statement,
obtaining locks, returning a status, client checking the status, etc.
That's just seems an all-around inefficient approach.
I assume that any RDBMS is smart enough, to notice, that Caches etc should not be recalculated (if nothing changes), if that is the problem.