if (empty($this->sql_from)) {
    // construct default SELECT and FROM clauses using parent relations
    $this->sql_select  = null;
    $this->sql_from    = null;
    $this->sql_groupby = null;
    $this->sql_having  = null;
    $where_str = $this->_sqlAssembleWhere($where, $where_array);
    // add code to obtain category data
    $this->sql_select .= ', categoria.fecini, categoria.fecfin';
    $this->sql_from   .= ' LEFT JOIN categoria ON (categoria.categoria_id=equipo.categoria_id)';
} // if