不明白的地方php

if(empty($_REQUEST[‘cont‘]) or is_null($_REQUEST[‘cont‘])){
        $sql = "select * from tb_article order by ".$fields." desc";
    }else{
        $querymem = $_REQUEST[‘querymem‘];
        $signslt = $_REQUEST[‘signslt‘];
        $cont = $_REQUEST[‘cont‘];
        $sql = ‘select * from tb_article ‘;       //firsttime
        if(in_array($querymem,array(‘id‘,‘hitnum‘,‘renum‘,‘examine‘))){
            $sql .= " where ".$querymem." ".$signslt." ".$cont;                //表示不懂
            
        }else if(in_array($querymem,array(‘firsttime‘))){
            if($signslt==‘=‘){
            $sql.= "where ".$querymem." like ‘%".$cont."%‘";
            }else{
            $sql .= " where ".$querymem." ".$signslt." ‘".$cont."‘";
            }
        }else if(in_array($querymem,array(‘typename‘,‘title‘,‘author‘))){
            if($signslt == ‘exac‘){
                $sql .= "where ".$querymem." = ‘".$cont."‘";
            }else if($signslt == ‘mist‘){
                $sql .= "where ".$querymem." like ‘%".$cont."%‘";
            }
        }
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