PHP PDO - single query for multiple x fields - php

Question

I have three fields, I need to update only the fields that are filled. The possible solution would be the following:
<?php
if(trim($_POST['field_1'])!='')
// query for update field 1
if(trim($_POST['field_2'])!='')
// query for update field 2
if(trim($_POST['field_3'])!='')
// query for update field 3
?>
But it is not the best optimization, Can you give me an example on how to do it with a single query using mysqli (with bind) or PDO?

Answer 1

You could build the query dynamically.
$fields = array();
foreach($_POST as $key => $value) {
// Only grab whitelisted fields
if (in_array($key, array('field_1', 'field_2', 'field_3'))) {
if (!empty(trim($value))) {
// Using the keys from $_POST assumes they are named after their database counterparts
$fields[$key] = trim($value);
}
}
}
// Grab the keys (fieldnames) so we can use them to build the query
$keys = array_keys($fields);
$sqlFieldsPart = implode(', ', array_map(function($field) {
return $field . '= :' . $field;
}, $keys));
$sql = sprintf('UPDATE tablename SET %s WHERE somefield=:somefield', $sqlFieldsPart);
$dbh = new PDO('mysql:hostname=localhost;dbname=yourdb', 'username', 'password');
$stmt = $dbh->prepare($sql);
// Modify keys on $fields
$data = array();
foreach ($fields as $key => $value) {
// Note the colon before the key variable, this is necessary
// It links to the placeholders in the query
$data[':' . $key] = $value;
}
// Set the value for the where clause
$data[':somefield'] = 'somevalue';
// Execute the statement, passing the data to the execute function
$stmt->execute($data);
This code assumes that your html fields are named after their database counterparts. If this is not the case, you can do the stuff from the first foreach loop hardcoded for each field or make some kind of field mapping.

Answer 2

I'm not sure if $_POST contains only the relevant fields or more, so I will assume you will find a way to isolate those in a $tmp array and use that instead.
I will also assume that you have already made a connection to the DB with PDO, and stored it in $db.
Finally, your row filter (where clause) is already built as a string in $rowfilter.
// trim all values
array_map('trim',$tmp);
// eliminate empty string values
$tmp=array_filter($tmp,function($el){return $el!='';});
// build the query string
$fields=array_map(function($el){$el="`$el`=?";},array_keys($tmp));
$fldstr=implode(',',$fields);
$sql="UPDATE `mytable` SET $fldstr WHERE $rowfilter";
// prepare and execute
$stmt = $db->prepare($sql);
$stmt->execute(array_values($tmp));