/**
* Get average value for field of records in database founded by sql-condition
*
* @param string $field_name
* @param string $condition
* @return float
*/
public function dbAverage($field, $condition = null)
{
$sql = $this->getModel()->_getSelectQuery_(null, $condition);
$sql = preg_replace("'select .* from 'si", "select avg(" . $this->getTableName() . "." . $field . ") as average from ", $sql);
if ($this->_SQL_DEBUG) {
die($sql);
}
$res = $this->_db->execSql($sql);
return is_array($res) ? $res[0]['average'] : null;
}
