Called to add the field to a query.
Overrides FieldPluginBase::query
public function query() {
$this
->ensureMyTable();
$this->node_table = $this->query
->ensure_table('node', $this->relationship);
$this->field_alias = $this->query
->add_field(NULL, "GREATEST(" . $this->node_table . ".changed, " . $this->tableAlias . ".last_comment_timestamp)", $this->tableAlias . '_' . $this->field);
}