theandystratton

<?php
/*
Place in theme's functions.php or /wp-content/mu-plugins folder
Assumes:
  - PHP 7
  - WP 5.2
  - Gravity Forms
  - Edit this file for the appropriate invite code => gform_id relationships (lines 32-37)
  - Edit this file for the appropriate invite code user meta key (line 41)
*/

theandystratton

<?php
// Sample code for reference

global $wpdb;

$year = (int) ( $_GET['year'] ?? date_i18n( 'Y' ) );

$sql = "SELECT * FROM transactions WHERE DATE( datetime_created ) LIKE %s";
$sql = $wpdb->prepare( $sql, $year . '-01-%' );