如何通过许多JOIN提高查询性能 [英] How to Improve Query Performance with many JOINs

问题描述

我有一个查询(目的是创建视图)，该查询使用一些联接来获取每一列.对于添加的每组联接，性能都会迅速下降(呈指数级?).

I have a query (with the purpose of making a view) which is using a few joins to get each column. Performance degrades quickly (exponentially?) for each set of joins added.

什么是使此查询更快的好方法?请在查询中查看评论.

What would be a good approach to make this query faster? Please see comments within the query.

如果有帮助，则使用的是WordPress DB模式.

If it helps, this is using the WordPress DB schema.

这是EXPLAIN的屏幕截图

Here is a screenshot of EXPLAIN

产品表

+--+----+
|id|name|
+--+----+
|1 |test|
+--+----+

元数据表

+----------+--------+-----+
|product_id|meta_key|value|
+----------+--------+-----+
|1         |price   |9.99 |
+----------+--------+-----+
|1         |sku     |ABC  |
+----------+--------+-----+

TERM_RELATIONSHIPS表

+---------+----------------+
|object_id|term_taxonomy_id|
+---------+----------------+
|1        |1               |
+---------+----------------+
|1        |2               |
+---------+----------------+

TERM_TAXONOMY表

+----------------+-------+--------+
|term_taxonomy_id|term_id|taxonomy|
+----------------+-------+--------+
|1               |1      |size    |
+----------------+-------+--------+
|2               |2      |stock   |
+----------------+-------+--------+

条款表

+-------+-----+
|term_id|name |
+-------+-----+
|1      |500mg|
+-------+-----+
|2      |10   |
+-------+-----+

查询

SELECT 
  products.id,
  products.name,
  price.value AS price,
  sku.value AS sku,
  size.name AS size
FROM products

/* These joins are performing quickly */

INNER JOIN `metadata` AS price ON products.id = price.product_id AND price.meta_key = 'price'
INNER JOIN `metadata` AS sku ON products.id = sku.product_id AND sku.meta_key = 'sku'

/* Here's the part that is really slowing it down - I run this chunk about 5 times with different strings to match */

INNER JOIN `term_relationships` AS tr ON products.id = tr.object_id
  INNER JOIN `term_taxonomy` AS tt
  ON tr.term_taxonomy_id = tt.term_taxonomy_id AND tt.taxonomy = 'size'
    INNER JOIN `terms` AS size
    ON tt.term_id = size.term_id

推荐答案

您的性能问题最有可能是由与"term_taxonomy"表的联接引起的.
所有其他联接似乎都使用主键(您可能在上面使用了工作索引).

因此，我的建议是在 term_taxonomy_id 和 term_id 上添加复合索引(或者如果您必须: taxonomy ).像这样:

Your performance issue is most likely caused by the join with the 'term_taxonomy' table.
All other joins seems to use the primary key (where you probobly have working indexes on).

So my suggestion is to add a compound index on term_taxonomy_id and term_id (or if you must: taxonomy). Like this:

CREATE UNIQUE INDEX idx_term_taxonomy_id_taxonomy
ON term_taxonomy( term_taxonomy_id, taxonomy);

希望这会对您有所帮助.

Hope this will help you.

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