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Question

使用此查询

SELECT
o1.created,
SEC_TO_TIME(TIMESTAMPDIFF(second, o1.created, (SELECT MAX(created) FROM orders o2 WHERE o2.created < o1.created and o2.created >= '2012-06-01'))) tsd
FROM
orders o1
WHERE o1.created >= '2012-06-01'
ORDER BY tsd DESC LIMIT 100

我想知道，如果有任何重要时间没有订单，这个时间跨度有多长。

以下是解释：

*************************** 1. row ***************************
           id: 1
  select_type: PRIMARY
        table: o1
         type: range
possible_keys: created
          key: created
      key_len: 4
          ref: NULL
         rows: 2649278
        Extra: Using where; Using index; Using filesort
*************************** 2. row ***************************
           id: 2
  select_type: DEPENDENT SUBQUERY
        table: o2
         type: range
possible_keys: created
          key: created
      key_len: 4
          ref: NULL
         rows: 2649278
        Extra: Using where; Using index

created的类型为timestamp。

查询现在运行了一个多小时。更改架构中的任何内容都不是一种选择。这是一次性查询，但我只是好奇是否可以提升性能。

Answer 1

尝试使用此查询。它更快吗？

SQLFiddle demo

select created,Previous_created,
       IF(tsd<>0,SEC_TO_TIME(tsd),0) as diff 
from
(
 select created,
       IF(@prev<>0,TIMESTAMPDIFF(second, @prev,created),0) tsd,
       @prev Previous_created,
       @prev:=created f2 
    from orders,(select @prev:=0) t1 
WHERE created >= '2012-06-01'
order by created
 ) t2 
order by tsd desc limit 100

Answer 2

我尝试使用没有子查询的解决方案：

select o1.created, TIMESTAMPDIFF(second, o1.created, o3.created) tsd 
from orders o1
inner join orders o2 on o2.created < o1.created and o2.created >= '2012-06-01'
left join orders o3 on o3.created > o2.created
where o1.created >= '2012-06-01' and o3.id is null;

如果created列被编入索引，可能要快得多。我担心diff列的排序不能在mysql中编入索引。

优化查询以查找订单之间的最大时间跨度

2 个答案:

SQLFiddle demo