Is there a MySQL function to 'use existing value' during update? - php

Question

Is there a way with MySQL to specify "use previous / inherit / no change / existing value"?
Rather than needing to pull the current data from the database and use it, or have a customized database function excluding editing those columns.
if(x > y) {
$role_id = 3;
} else {
$role_id = '#no-change'; // Is there a way to do this? (not proper SQL syntax)
}
$update_user = $this->db->update('users',
array(
'first_name' => filterName($post['first_name']),
'last_name' => filterName($post['last_name']),
'email' => filterEmail($post['email']),
'role_id' => $role_id,
), $user_id_to_edit, 'user_id');
In a case like this where the db function is using prepared statements (not shown) I can't use the column name as to reflect the current value.
Is there such a MySQL function / variable that will essentially "ignore" updating that column? (just leave the existing value)
UPDATE: Here's the Update function:
public function update($table, $data, $where_id, $column = 'user_id') {
// Check for $table or $data not set
if (( empty( $table ) || empty( $data )) || empty($data) ) {
return false;
}
// Initiate variable to append to
$placeholders ='';
// Parse data for column and placeholder names
foreach ($data as $key => $value) {
$placeholders .= sprintf('%s=:%s,', $key, $key);
}
// Trim excess commas
$placeholders = rtrim($placeholders, ',');
// Append where ID to $data
$data['where_id'] = $where_id;
// Prepary our query for binding
$stmt = $this->db->prepare("UPDATE {$table} SET {$placeholders} WHERE $column = :where_id");
// Execute the query
$stmt->execute($data);
// Check for successful insertion
if ( $stmt->rowCount() ) {
return true;
}
return false;
}

Answer 1

You could try this:
$data = array(
'first_name' => filterName($post['first_name']),
'last_name' => filterName($post['last_name']),
'email' => filterEmail($post['email']))
if(x > y) {
$data['role_id'] = 3;
}
$update_user = $this->db->update('users', $data, $user_id_to_edit, 'user_id');
That way, you can customize $data before hand if you like.
I should also mention, if you're concerned about redundancy, you can put your data sanitation inside a function. Something along the lines of:
function sanitize($data) {
if(x > y) {
$data['role_id'] = 3;
} else {
if(isset($data['role_id']) {
unset($data['role_id']);
}
}
return $data;
}
$data = array(
'first_name' => filterName($post['first_name']),
'last_name' => filterName($post['last_name']),
'email' => filterEmail($post['email']))
$update_user = $this->db->update('users', sanitize($data), $user_id_to_edit, 'user_id');
Edit: Something I should mention is that, if we're talking pure SQL, all you need to do is omit those columns from the query, so:
UPDATE table SET Col1=val1, Col2=val2, Col3=val3 WHERE id=val
But if for some reason you don't want to update Col3, just remove it from the query:
UPDATE table SET Col1=val1, Col2=val2 WHERE id=val
Since you have a function that just adds whatever you give it, you just need to sanitize the data ahead of time. That's probably the best way to do it.