mysql in 查询优化

2014年11月29日21:01:01

场景：有的时候查询数据库的select in 语句中会有非常多不连续的数值，会很影响查询效率

方法：将select in 查询转换成多个select between and 语句

代码：核心代码(id要排过顺序)

     public function group()
     {
         // $a = array(1,2,3,5,7,8,9);
         $a = array(1,3,4,5,7,8,9);
         $len = count($a);
         $cur = 0; //当前遍历元素的下标
         $pre = $a[0]; //前一个元素的值

         $new = array('0' => array($a[0]));
         for ($i = 1; $i < $len; $i++) {
             if (($a[$i] - $pre) == 1 ) {
                 $new[$cur][] = $a[$i];
             } else {
                 $cur = $i;
                 $new[$cur][] = $a[$i];
             }
             $pre = $a[$i];
         }

         print_r($new);
     }

//结果

 Array
 (
     [0] => Array
         (
             [0] => 1
         )

     [1] => Array
         (
             [0] => 3
             [1] => 4
             [2] => 5
         )

     [4] => Array
         (
             [0] => 7
             [1] => 8
             [2] => 9
         )

 )

完整代码:

 //select in
     //arrData 整数数组，最好是整数
     public function select_in($key, $arrData, $fields='')
     {
         $fields = $fields ? $fields : '*';
         sort($arrData);
         $len = count($arrData);
         $cur = 0;
         $pre = $arrData[0];

         $new = array('0' => array($arrData[0]));
         for ($i = 1; $i < $len; $i++) {
             if (($arrData[$i] - $pre) == 1 ) {
                 $new[$cur][] = $arrData[$i];
             } else {
                 $cur = $i;
                 $new[$cur][] = $arrData[$i];
             }
             $pre = $arrData[$i];
         }

         $arrSql = array();
         foreach ($new as $v) {
             $len = count($v) - 1;
             if ($len) {
                 $s = $v[0];
                 $e = end($v);
                 $sql = "(select $fields from {$this->_dt} where $key between $s and $e)";
             } else {
                 $s = $v[0];
                 $sql = "(select $fields from {$this->_dt} where $key = $s)";
             }

             $arrSql[] = $sql;
         }

         $strUnion = implode(' UNION ALL ', $arrSql);
         $res = $this->query($strUnion);
         return $this->rstoarray($res);
     }

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