ayuda por favorrrrrrrrr

[aimar_20]

lo he intentado tb, pero no lo he conseguido, te pongo el codigo que he puesto

case 'unknown':
$_pagi_sql="select r.*, b.*,j.*,c.*,t.*,th.*,m.* ((from referencia r left join book b)";
$_pagi_sql.="left join book b on r.Id_Reference=b.Id_Rerence ";
$_pagi_sql.="left join journal j on r.Id_Reference=j.Id_Reference ";
$_pagi_sql.="left join conferencia c on r.Id_Reference=c.Id_Reference ";
$_pagi_sql.="left join thecnical_report t on r.Id_Reference=t.Id_Reference ";
$_pagi_sql.="left join thesis th on r.Id_Reference=th.Id_Reference ";
$_pagi_sql.="left join miscellaneous m on r.Id_Reference=m.Id_Reference) ";
$_pagi_sql.="where ";

if (!empty($title)) $_pagi_sql.= "r.Title like '%".$title."%'";

if (!empty($author)) $_pagi_sql.= "AND r.Author like '%".$author."%'";

if (!empty($year)) $_pagi_sql.="AND r.Year like '%".$year."%'";

if ($month!="no")
{
switch($month)
{
case "january": $_pagi_sql.= "AND r.Month like '%january%'";break;
case "february": $_pagi_sql.= "AND r.Month like '%february%'";break;
case "march": $_pagi_sql.= "AND r.Month like '%march%'";break;
case "april": $_pagi_sql.= "AND r.Month like '%april%'";break;
case "maig": $_pagi_sql.= "AND r.Month like '%maig%'";break;
case "june": $_pagi_sql.= "AND r.Month like '%june%'";break;
case "july": $_pagi_sql.= "AND r.Month like '%july%'";break;
case "august": $_pagi_sql.= "AND r.Month like '%august%'";break;
case "september": $_pagi_sql.= "AND r.Month like '%september%'";break;
case "october": $_pagi_sql.= "AND r.Month like '%october%'";break;
case "november": $_pagi_sql.= "AND r.Month like '%november%'";break;
case "december": $_pagi_sql.= "AND r.Month like '%december%'";break;
}
}

break;
esto todo forma parte de un switch. He probao hacer la consulta de varias formas pero, supongo que no la estoy haciendo bien, o tendre algun error.

gracias