php链式操作

重点是每个方法都返回$this

<?php
class sql{
     private $sql=array(
            "from"=>"",
            "where"=>"",
            "order"=>"",
            "limit"=>""
        );

     public function from($tableName) {
         $this->sql["from"]="FROM ".$tableName;
         return $this;
     }

     public function where($_where='1=1') {
         $this->sql["where"]="WHERE ".$_where;
         return $this;
       }

     public function order($_order='id DESC') {
         $this->sql["order"]="ORDER BY ".$_order;
         return $this;
     }

     public function limit($_limit='30') {
         $this->sql["limit"]="LIMIT 0,".$_limit;
         return $this;
     }
     public function select($_select='*') {
         return "SELECT ".$_select." ".(implode(" ",$this->sql));
     }
 }

 $sql =new sql();

 echo $sql->from("testTable")->where("id=1")->order("id DESC")->limit(10)->select();
 //输出 SELECT * FROM testTable WHERE id=1 ORDER BY id DESC LIMIT 0,10