Meta Query for specific months

Question

I have a custom field which stores a date in a timestamp. I want to run a query that display posts based on the month, for example all entries from March, the specific day or year doesn't matter. I'm guessing i need to use the DATE or the DATETIME type for the meta query, but i don't know how to proceed:

if ($_GET['month']) {
    $meta_query[] = array(
            'key' => 'event_start_date',
            'value' => $_GET['month']
    );
}

$args = array(
    'post_type' => 'event',
    'paged' => $paged,
    'posts_per_page' => -1,
    'tax_query' => $cleanArray,
    'meta_key' => 'event_start_date',
    'orderby' => 'meta_value_num',
    'order' => 'DESC',
    'meta_query'=> $meta_query
);

$events = new WP_Query($args);

Answer 1

You need the 2 digit month number that you want to query on and then use the code below. This should be easy with php (for example, see this post). In the code below $month is the number of the month in a 2 digit format, eg March would be 03.

$start_date = date('Y'.$month.'01'); // First day of the month
$end_date = date('Y'.$month.'t'); // 't' gets the last day of the month

$meta_query = array(
    'key'       => 'event_start_date',
    'value'     => array($start_date, $end_date),
    'compare'   => 'BETWEEN',
    'type'      => 'DATE'
);

Answer 2

For Date Time just add eg. 00:00:00 - 23:00:00

$month      = $_GET['month'];
$start_date = date( 'Y-' . $month . '-01 00:00:00' );
$end_date   = date( 'Y-' . $month . '-t 23:00:00', strtotime( $start_date ) );

$meta_query = array(
    'key'       => 'event_start_date',
    'value'     => array($start_date, $end_date),
    'compare'   => 'BETWEEN',
    'type'      => 'DATETIME'
);

Answer 3

WordPress 3.7 introduced the date_query to display posts by month:

$args = array(
    'date_query' => array(
        array(
            'month' => $month
        )
    )
);
$query = new WP_Query( $args );