为什么我的查询这么慢？试图在mysql中的左连接上查找空字段

编辑：更新了Bill Karwin的建议。还是很慢

我正在尝试编写一个查询，该查询将查找订单上输入到仓库的所有项目，该仓库中没有该项目的记录。例如，如果为仓库A输入了项目XYZ，但仓库A实际上没有携带项目XYZ，我希望订单项目显示在我的报告中

我可以很好地运行查询，但这似乎需要很长时间（50秒）。它似乎主要取决于where子句中的“is null”条件。如果我删除带有“isnull”的条件并运行它，它将在大约4.8秒内执行。我的问题是：

SELECT
saw_order.Wo,
saw_orderitem.Item,
saw_orderitem.Stock,
saw_order.`Status`,
saw_order.`Date`,
saw_orderitem.Warehouse,
saw_stockbalance.Balno,
saw_stockbalance.Stock
FROM
saw_order
Inner Join saw_orderitem ON saw_order.Wo = saw_orderitem.Wo
Inner Join saw_stock ON saw_orderitem.Stock = saw_stock.Stock
Left Join saw_stockbalance ON saw_orderitem.Stock = saw_stockbalance.Stock 
    AND saw_orderitem.Warehouse = saw_stockbalance.Warehouse
WHERE
saw_order.`Status` Between 3 and 81 and
saw_stockbalance.Stock Is Null

当我解释上面的查询时，我看到：

+----+-------------+------------------+--------+------------------------------+---------+---------+-------------------------------------------------------+-------+-------------------------+
| id | select_type | table            | type   | possible_keys                | key     | key_len | ref                                                   | rows  | Extra                   |
+----+-------------+------------------+--------+------------------------------+---------+---------+-------------------------------------------------------+-------+-------------------------+
|  1 | SIMPLE      | saw_stock        | index  | PRIMARY                      | PRIMARY | 17      | NULL                                                  | 32793 | Using index             |
|  1 | SIMPLE      | saw_orderitem    | ref    | PRIMARY,Stock,StockWarehouse | Stock   | 17      | saws.saw_stock.Stock                                  |    68 |                         |
|  1 | SIMPLE      | saw_order        | eq_ref | PRIMARY,Status               | PRIMARY | 4       | saws.saw_orderitem.Wo                                 |     1 | Using where             |
|  1 | SIMPLE      | saw_stockbalance | ref    | Stock,Warehouse              | Stock   | 20      | saws.saw_orderitem.Stock,saws.saw_orderitem.Warehouse |     1 | Using where; Not exists |
+----+-------------+------------------+--------+------------------------------+---------+---------+-------------------------------------------------------+-------+-------------------------+

---

我很确定我的联接中各个表的所有字段都有索引，但我不知道如何重写查询以加快查询速度

编辑：以下是我在表格上设置的索引：

mysql> show index from saw_order;
+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table     | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| saw_order |          0 | PRIMARY  |            1 | Wo          | A         |      553425 | NULL     | NULL   |      | BTREE      |         |
| saw_order |          1 | Customer |            1 | Customer    | A         |       14957 | NULL     | NULL   |      | BTREE      |         |
| saw_order |          1 | Other    |            1 | Other       | A         |         218 | NULL     | NULL   |      | BTREE      |         |
| saw_order |          1 | Site     |            1 | Site        | A         |           8 | NULL     | NULL   |      | BTREE      |         |
| saw_order |          1 | Date     |            1 | Date        | A         |        1594 | NULL     | NULL   |      | BTREE      |         |
| saw_order |          1 | Status   |            1 | Status      | A         |          15 | NULL     | NULL   |      | BTREE      |         |
+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
6 rows in set

mysql> show index from saw_orderitem;
+---------------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table         | Non_unique | Key_name       | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+---------------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| saw_orderitem |          0 | PRIMARY        |            1 | Wo          | A         | NULL        | NULL     | NULL   |      | BTREE      |         |
| saw_orderitem |          0 | PRIMARY        |            2 | Item        | A         |     1842359 | NULL     | NULL   |      | BTREE      |         |
| saw_orderitem |          1 | Stock          |            1 | Stock       | A         |       27093 | NULL     | NULL   |      | BTREE      |         |
| saw_orderitem |          1 | Product        |            1 | Product     | A         |         803 | NULL     | NULL   |      | BTREE      |         |
| saw_orderitem |          1 | GGroup         |            1 | GGroup      | A         |         114 | NULL     | NULL   |      | BTREE      |         |
| saw_orderitem |          1 | ShipVia        |            1 | ShipVia     | A         |         218 | NULL     | NULL   |      | BTREE      |         |
| saw_orderitem |          1 | Warehouse      |            1 | Warehouse   | A         |           9 | NULL     | NULL   |      | BTREE      |         |
| saw_orderitem |          1 | StockWarehouse |            1 | Stock       | A         |       27093 | NULL     | NULL   |      | BTREE      |         |
| saw_orderitem |          1 | StockWarehouse |            2 | Warehouse   | A         |       49793 | NULL     | NULL   |      | BTREE      |         |
+---------------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
9 rows in set

mysql> show index from saw_stock;
+-----------+------------+-------------------+--------------+-------------------+-----------+-------------+----------+--------+------+------------+---------+
| Table     | Non_unique | Key_name          | Seq_in_index | Column_name       | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-----------+------------+-------------------+--------------+-------------------+-----------+-------------+----------+--------+------+------------+---------+
| saw_stock |          0 | PRIMARY           |            1 | Stock             | A         |       32793 | NULL     | NULL   |      | BTREE      |         |
| saw_stock |          1 | Class             |            1 | Class             | A         |         655 | NULL     | NULL   | YES  | BTREE      |         |
| saw_stock |          1 | DateFirstReceived |            1 | DateFirstReceived | A         |        2732 | NULL     | NULL   |      | BTREE      |         |
+-----------+------------+-------------------+--------------+-------------------+-----------+-------------+----------+--------+------+------------+---------+
3 rows in set

mysql> show index from saw_stockbalance;
+------------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table            | Non_unique | Key_name  | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+------------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| saw_stockbalance |          0 | PRIMARY   |            1 | Balno       | A         |      146315 | NULL     | NULL   |      | BTREE      |         |
| saw_stockbalance |          1 | Stock     |            1 | Stock       | A         |       36578 | NULL     | NULL   |      | BTREE      |         |
| saw_stockbalance |          1 | Stock     |            2 | Warehouse   | A         |      146315 | NULL     | NULL   |      | BTREE      |         |
| saw_stockbalance |          1 | Warehouse |            1 | Warehouse   | A         |          11 | NULL     | NULL   |      | BTREE      |         |
+------------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
4 rows in set

有什么想法吗？

我会尽量让它用一个。也就是说，不是测试

Balno

是否为null，而是测试左侧外部联接条件中的一列是否为null。例如

库存

或

仓库

您还应该在两个表中的两列（

Stock

，

Warehouse

）上定义索引

saw_orderitem

和

saw_stockbalance

，

Try:

SELECT t.wo,
       soi.item,
       soi.stock,
       t.Status,
       t.Date,
       soi.warehouse,
       NULL 'balno',  --ssb.Balno,
       NULL 'stock', --ssb.Stock
  FROM SAW_ORDER t
  JOIN SAW_ORDERITEM soi ON soi.wo = t.wo
  JOIN SAW_STOCK ss ON ss.stock = soi.stock
 WHERE t.status BETWEEN 3 AND 81 
   AND NOT EXISTS (SELECT NULL
                     FROM SAW_STOCKBALANCE ssb
                    WHERE ssb.stock != soi.stock
                      AND ssb.warehouse = soi.warehouse)

查询的问题是，您正在检查左联接上是否有null…
“我非常确定我的联接中各个表的所有字段都有索引”这是什么类型的语句？您在这些表上的确切索引是什么？很抱歉非语句：-）。我已经用索引信息更新了我的帖子。我在saw_stockbalance表中有一个覆盖索引，但在saw_orderitem表中没有。我将把覆盖索引添加到我的saw_orderitem表中，看看我得到了什么。谢谢FWIW，我经常发现MySQL中的外部连接比内部连接慢一些。当然，任何类型的连接都比根本不进行连接要慢。但显然50秒太多了。谢谢你的帮助。该查询仍然非常慢，但有人将我指向数据库中的另一个表，该表正好包含我需要的内容，并允许我在.047s中执行查询！是的，在您实际确定了瓶颈之后，非规范化（或重复）数据并没有什么问题。