WordPress function for deleting all transients related to a certain namespace

delete_transients.php

<?php

// Purge all the transients associated with our plugin.
function purge() {

  global $wpdb;

  $prefix = esc_sql( $this -> get_transient_prefix() );

  $options = $wpdb -> options;

  $t  = esc_sql( "_transient_timeout_$prefix%" );

  $sql = $wpdb -> prepare (
    "
      SELECT option_name
      FROM $options
      WHERE option_name LIKE '%s'
    ",
    $t
  );

  $transients = $wpdb -> get_col( $sql );

  // For each transient...
  foreach( $transients as $transient ) {

    // Strip away the WordPress prefix in order to arrive at the transient key.
    $key = str_replace( '_transient_timeout_', '', $transient );

    // Now that we have the key, use WordPress core to the delete the transient.
    delete_transient( $key );

  }
  
}

?>