mysql left 二分查找

//内链接
 SELECT * FROM table1,table2 WHERE table1.id=table2.id;  
 
 //left join
 SELECT * FROM table1 LEFT JOIN table2 ON table1.id=table2.id;  
 
 //3表查询  
 SELECT * FROM table1 LEFT JOIN table2 ON table1.id=table2.id  
 LEFT JOIN table3 ON table2.id=table3.id;  
//二分查找
 function binarySearch($arr,$target){
 $low = 0;
       $high = count($arr)-1;
       while($low<=$high){
           $mid = intval(($low+$high)/2);
   #找到元素
       if ($arr[$mid]) == $target) return $mid;
 #中元素比目标大,查找左部
           if ($arr[$mid] > $target) $high = $mid-1;
 #中元素比目标小,查找右部
           if ($arr[$mid] < $target) $low = $mid+1;
             }  
    
            #查找失败
         return false;
 
 }
      $arr = array(1, 3, 5, 7, 9, 11);
      $inx = binarySearch($arr, 1);
      var_dump($inx);