Escapes an alias name string.
Force all alias names to be strictly alphanumeric-plus-underscore. In contrast to DatabaseConnection::escapeField() / DatabaseConnection::escapeTable(), this doesn't allow the period (".") because that is not allowed in aliases.
string The sanitized field name string.
public function escapeAlias($field) {
if (!isset($this->escapedAliases[$field])) {
$this->escapedAliases[$field] = preg_replace('/[^A-Za-z0-9_]+/', '', $field);
}
return $this->escapedAliases[$field];
}