mysql in 查詢優化

2014年11月29日21:01:01

場景：有的時候查詢數據庫的select in 語句中會有非常多不連續的數值，會很影響查詢效率

方法：將select in 查詢轉換成多個select between and 語句

代碼：核心代碼(id要排過順序)

    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; //當前遍歷元素的下標
        $pre = $a[0]; //前一個元素的值

        $new = array('0' => array($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);
    }

//結果

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

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

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

)

 完整代碼:

//select in
    //arrData 整數數組，最好是整數
    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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