mysql解释结果解释

下面的查询与我期望的完全一样，直观且不生成中间表。缺点是需要很长时间才能完成

在这种情况下，我要做的是分步分解查询并创建那些中间表和索引。这一次，我想更好地处理explain提供的提示，并希望得到任何提示：我在下面的查询中遗漏了哪些明显的优化步骤

按照中的建议，我在

订单原始

中创建了关于

订单编号

、

订单类型

和

项目

的索引。然而，尚不清楚这些将如何进行字符处理/正则表达式

SELECT bundle_headers.order_number , bundle_headers.title , digital_subs.subscription_id , 1 as bundle_component
from
(
  select order_number , substring( item , 1 , 3 ) as title , quantity from orders_raw
  where order_type in (4,6)                      
) bundle_headers
inner join
(
  select order_number , subscription_id , item as title , quantity from orders_raw
  where order_type = 0 and length( item ) = 4    
) digital_subs
on bundle_headers.order_number = digital_subs.order_number and
   digital_subs.title regexp concat( '.*' , bundle_headers.title , '.*' ) and
   bundle_headers.quantity = digital_subs.quantity

UNION


SELECT bundle_headers.order_number , bundle_headers.title , print_subs.subscription_id , 1 as bundle_component
from
(
  select order_number , substring( item , 1 , 3 ) as title , quantity from orders_raw
  where order_type in (4,6)                      
) bundle_headers
inner join
(
  select order_number , subscription_id , item as title , quantity from orders_raw
  where order_type = 0 and length( item ) = 3    
) print_subs
on bundle_headers.order_number = print_subs.order_number and
   print_subs.title regexp concat( '.*' , bundle_headers.title , '.*' ) and
   bundle_headers.quantity = print_subs.quantity;

编辑，@tin tran：我还没有严格地对上面的查询和您的查询（经过几次更正后，复制到下面）在空闲机器上开始计时。我确实提交了它，并且没有看到运行时间的明显减少

 SELECT bundle_headers.order_number,
   substring(bundle_headers.item,1,3) as title,
   subs.subscription_id,
   1 as bundle_component
 FROM orders_raw bundle_headers
 INNER JOIN orders_raw subs ON (bundle_headers.order_number = subs.order_number)
 WHERE (bundle_headers.order_type = 4 OR bundle_headers.order_type = 6)
   AND subs.order_type = 0
   AND bundle_headers.quantity = subs.quantity
   AND subs.item LIKE CONCAT('%',substring(bundle_headers.item,1,3),'%')
   AND (length(subs.item) = 4 OR length(subs.item) = 3)

---

请尝试此查询，看看是否产生相同的结果。如果再快一点呢

SELECT bundle_headers.order_number,substring(bundle_headers.title,1,3) as title,subs.subscription_id,1 as bundle_component
FROM order_type bundle_headers
INNER JOIN orders_raw subs ON (bundle_headers.order_number = subs.order_number)
WHERE (bundle_headers.order_type = 4 OR bundle_headers.order_type = 6)
  AND subs.order_type = 0
  AND bundle_headers.quantity = subs.quantity
  AND subs.title LIKE CONCAT('%',substring(bundle_headers.title,1,3),'%')
  AND (length(subs.item) = 4 OR length(subs.item) = 3)

---

虽然您的问题是关于

解释
，但我建议您创建临时表并使用它们而不是子查询。。。我用过这种方法，它加快了速度。当然，您需要为临时表创建适当的索引：
drop table if exists temp_myTable；创建临时表temp_myTable select；alter table temp_myTable添加索引idx_anIndex（外地）@Barranka-临时表而不是子查询？更快？？我第一次听到这个…@Tomas信不信由你。。。我已经多次面临这种任务，在大多数情况下，创建中间临时表比子查询更快。当然，必须小心地创建它们，并且需要对它们进行适当的索引。很普通，但它完成了任务。