Error: mysqli_query()
select distinct(ACCO_CONGRESO), CON_NOMBRE from actividad_congreso, congreso where acco_tipo_actividad = 'Conference Chair' and ACCO_CONGRESO = CON_ACRONIMO and ACCO_PERSONA like 'Xavier Ferré' order by IFNULL(CON_CLASIF, 'Z'), CON_ORDEN, ACCO_CONGRESO