Question

The following code needs to make use of 3 variables given by the user. By default all of these variables equal to 0.

1. time (textbox)
2. city (drop down list)
3. type (drop down list)

If for example time and city is given by the user, but lets the type zero, it will not return any results.
My question is what is an effective and efficient way to modify my existing code so that if the user chooses not to select time, city or type or any combination of these, there will be results returned?

For example if time 21:00 is added with city number 3, it will show all the types that meet the 2 criteria should be listed.

$question= 'SELECT * FROM events WHERE ABS(TIMESTAMPDIFF( HOUR , `time`, :time )) < 2 AND city=:city AND type=:type';
$query = $db->prepare($question);
$query->bindValue(":time", $time, PDO::PARAM_INT);
$query->bindValue(":city", $city, PDO::PARAM_INT);
$query->bindValue(":type", $type, PDO::PARAM_INT);
$query->execute();

Answer 1

<?php
$question= 'SELECT * FROM events WHERE ';

$hasTime = false;
if(!empty($time)) { // @note better validation here
    $hasTime = true;
    $question .= 'ABS(TIMESTAMPDIFF( HOUR , `time`, :time )) < 2 ';
}

$hasCity = false;
if(!empty($city)) { // @note better validation here
    $hasCity = true;
    $question .= 'AND city=:city ';
}

$hasType = false;
if(!empty($type)) { // @note better validation here
    $hasType = true;
    $question .= 'AND type=:type';
}

$query = $db->prepare($question);

if($hasTime)
    $query->bindValue(":time", $time, PDO::PARAM_INT);
if($hasCity)
    $query->bindValue(":city", $city, PDO::PARAM_INT);
if($hasType)
    $query->bindValue(":type", $type, PDO::PARAM_INT);

$query->execute();
$results = $query->fetchAll();

if(empty($results))
    echo 'no results';
else
    // $results is an array of arrays