Question

目前，我们正在使用自定义CI库从我们数据库中作为数据库记录存在的文档生成PDF文件。

每个文档都与具有一对多关系的内容（==行）相关。每行都有一个数字（字段：row_span），表示在PDF中打印后将使用的行数。

每个获得构建的PDF页面，仅使用子查询选择该页面所需的行：

$where = $this->docType."_id = ".$this->data['doc']->id." AND visible = 1";
$sql = "SELECT *,

    (SELECT
    sum(row_span) FROM app_".$this->docType."_rows X
    WHERE X.position <= O.position 
    AND ".$where." 
    ORDER BY position ASC) 'span_total'

    FROM app_".$this->docType."_rows O 
    WHERE ".$where."
    HAVING span_total > ".(($i-1)*$this->maxRows)." AND span_total <= ".($i*$this->maxRows)." ORDER BY O.position ASC ";

$rows = $rows->query($sql);

在代码中$i是页码，并且从文档模板记录中加载$this->maxRows，表示PDF模板有多少行。

因此，当SQL呈现时，对于ID为834的订单的第1页，它可能看起来像这样：

SELECT `app_order_rows`.*, 
(SELECT SUM(`app_order_rows_subquery`.`row_span`) AS row_span
    FROM `app_order_rows` `app_order_rows_subquery`
    WHERE `app_order_rows_subquery`.`position` <= 'app_order_rows.position'
    AND `app_order_rows_subquery`.`order_id` =  834
    AND `app_order_rows_subquery`.`visible` =  1
    ORDER BY `app_order_rows_subquery`.`position` asc) AS span_total 
FROM (`app_order_rows`) 
WHERE `app_order_rows`.`order_id` =  834
AND `app_order_rows`.`visible` =  1
HAVING span_total >  0
AND span_total <=  45
ORDER BY `app_order_rows`.`position` asc

使用EXPLAIN运行它会将此作为输出：

+====+=============+=========================+======+===============+======+=========+======+======+=============================+===+
| id | select_type | table                   | type | possible_keys | key  | key_len | ref  | rows | Extra                       |   |
+====+=============+=========================+======+===============+======+=========+======+======+=============================+===+
| 1  | PRIMARY     | app_order_rows          | ALL  | NULL          | NULL | NULL    | NULL | 1809 | Using where; Using filesort | 1 |
+----+-------------+-------------------------+------+---------------+------+---------+------+------+-----------------------------+---+
| 2  | SUBQUERY    | app_order_rows_subquery | ALL  | NULL          | NULL | NULL    | NULL | 1809 | Using where                 | 2 |
+====+=============+=========================+======+===============+======+=========+======+======+=============================+===+

这很有效，但是......当我们有大量订单或发票时，它会使文档变得非常慢。这可能是由子查询引起的。

有没有人知道如何在没有子查询的情况下进行相同的选择？也许我们将不得不采用一种全新的方法来选择行并构建PDF。我们愿意接受建议^^

提前致谢

------------------------------- edit --------------- ---------------

索引创建后的EXPLAIN：

+====+=============+=========================+=======+===============+============+=========+=======+======+=============+===+
| id | select_type | table                   | type  | possible_keys | key        | key_len | ref   | rows | Extra       |   |
+====+=============+=========================+=======+===============+============+=========+=======+======+=============+===+
| 1  | PRIMARY     | app_order_rows          | ref   | index_main    | index_main | 5       | const | 9    | Using where | 1 |
+----+-------------+-------------------------+-------+---------------+------------+---------+-------+------+-------------+---+
| 2  | SUBQUERY    | app_order_rows_subquery | range | index_main    | index_main | 10      | NULL  | 1    | Using where | 2 |
+====+=============+=========================+=======+===============+============+=========+=======+======+=============+===+

Answer 1

正如您在评论中所确认的那样，这些表没有索引。

立即解决方案是：

create index index_main on app_order_rows (order_id, position);

使用子查询优化SQL并使用

1 个答案: