php - 为这个简单的代码减少许多 SQL 查询

Question

我有一个包含事件开始日期的数据库表。一个事件在下一个事件开始时结束。给定开始日期和结束日期，我希望创建一个具有相应事件 ID 的日期数组。

目前我为每个日期运行一个 SQL 查询。伪代码：

$currDate = $startDate
While $currDate++ < $endDate
  echo $currDate . " - " . dbQuery("SELECT TOP 1 ID FROM events WHERE eventDate <= '$currDate' ORDER BY eventDate DESC");
Loop

我怎样才能提高效率（在 PHP 中）？

编辑：感谢您的回答，但我意识到问题并不清楚。设法编写了一些在我的服务器上快速执行（<10ms）的 SQL，日期跨度为数年。

score 2 · Accepted Answer

select distinct
e1.eventDate,
ID = (
        select top 1 e2.ID 
        from Events e2 
        where e2.eventDate <= e1.eventDate 
        order by e2.eventDate desc
    )
from 
Events e1

当您从查询中获取结果时，您会在代码中循环它们并显示结果。使您的实现更高效的关键是减少数据库往返次数。

score 1 · Accepted Answer

您可以使用类似下面的查询，这样您将一次检索整个事件 ID、日期开始和结束日期列表：

select id, date_start,(select min(date_start) from eventss where date_start > e.date_start) as date_end from
eventss e where date_start >= @DateStart
and 
(select min(date_start) from eventss 
where date_start > e.date_start) <= @DateEnd

score 0 · Accepted Answer

这是使用 SQL 的解决方案：

SQL小提琴

MS SQL Server 2008 架构设置：

Create Table dbo.Events (
  ID int not null primary key nonclustered,
  EventDate datetime not null
);


Insert Into dbo.Events (ID, EventDate) Values
  (1, '2011-11-19'),
  (2, '2011-11-25'),
  (3, '2011-12-12'),
  (4, '2012-01-02'),
  (5, '2012-01-05'),
  (6, '2012-02-10');

查询 1：

DECLARE @dtStart DATETIME,
        @dtEnd   DATETIME

SET @dtStart = '2011-11-01'
SET @dtEnd = '2012-02-20'

SELECT thedate,
       eventID = (SELECT TOP 1 id
                  FROM   events
                  WHERE  eventdate <= thedate
                  ORDER  BY eventdate DESC)
FROM   (SELECT Dateadd(DAY, number, @dtStart) AS theDate --build dates from the start to end date
        FROM   (SELECT DISTINCT number
                FROM   master.dbo.spt_values
                WHERE  name IS NULL) n --returns integer values from 0 to 2037
        WHERE  Dateadd(DAY, number, @dtStart) < @dtEnd) x

结果：

|                         THEDATE | EVENTID |
---------------------------------------------
| November, 01 2011 00:00:00+0000 |  (null) |
| November, 02 2011 00:00:00+0000 |  (null) |
| November, 03 2011 00:00:00+0000 |  (null) |
| November, 04 2011 00:00:00+0000 |  (null) |
| November, 05 2011 00:00:00+0000 |  (null) |
| November, 06 2011 00:00:00+0000 |  (null) |
| November, 07 2011 00:00:00+0000 |  (null) |
| November, 08 2011 00:00:00+0000 |  (null) |
| November, 09 2011 00:00:00+0000 |  (null) |
| November, 10 2011 00:00:00+0000 |  (null) |
| November, 11 2011 00:00:00+0000 |  (null) |
| November, 12 2011 00:00:00+0000 |  (null) |
| November, 13 2011 00:00:00+0000 |  (null) |
| November, 14 2011 00:00:00+0000 |  (null) |
| November, 15 2011 00:00:00+0000 |  (null) |
| November, 16 2011 00:00:00+0000 |  (null) |
| November, 17 2011 00:00:00+0000 |  (null) |
| November, 18 2011 00:00:00+0000 |  (null) |
| November, 19 2011 00:00:00+0000 |       1 |
| November, 20 2011 00:00:00+0000 |       1 |
| November, 21 2011 00:00:00+0000 |       1 |
| November, 22 2011 00:00:00+0000 |       1 |
| November, 23 2011 00:00:00+0000 |       1 |
| November, 24 2011 00:00:00+0000 |       1 |
| November, 25 2011 00:00:00+0000 |       2 |
| November, 26 2011 00:00:00+0000 |       2 |
| November, 27 2011 00:00:00+0000 |       2 |
| November, 28 2011 00:00:00+0000 |       2 |
| November, 29 2011 00:00:00+0000 |       2 |
| November, 30 2011 00:00:00+0000 |       2 |
| December, 01 2011 00:00:00+0000 |       2 |
| December, 02 2011 00:00:00+0000 |       2 |
| December, 03 2011 00:00:00+0000 |       2 |
| December, 04 2011 00:00:00+0000 |       2 |
| December, 05 2011 00:00:00+0000 |       2 |
| December, 06 2011 00:00:00+0000 |       2 |
| December, 07 2011 00:00:00+0000 |       2 |
| December, 08 2011 00:00:00+0000 |       2 |
| December, 09 2011 00:00:00+0000 |       2 |
| December, 10 2011 00:00:00+0000 |       2 |
| December, 11 2011 00:00:00+0000 |       2 |
| December, 12 2011 00:00:00+0000 |       3 |
| December, 13 2011 00:00:00+0000 |       3 |
| December, 14 2011 00:00:00+0000 |       3 |
| December, 15 2011 00:00:00+0000 |       3 |
| December, 16 2011 00:00:00+0000 |       3 |
| December, 17 2011 00:00:00+0000 |       3 |
| December, 18 2011 00:00:00+0000 |       3 |
| December, 19 2011 00:00:00+0000 |       3 |
| December, 20 2011 00:00:00+0000 |       3 |
| December, 21 2011 00:00:00+0000 |       3 |
| December, 22 2011 00:00:00+0000 |       3 |
| December, 23 2011 00:00:00+0000 |       3 |
| December, 24 2011 00:00:00+0000 |       3 |
| December, 25 2011 00:00:00+0000 |       3 |
| December, 26 2011 00:00:00+0000 |       3 |
| December, 27 2011 00:00:00+0000 |       3 |
| December, 28 2011 00:00:00+0000 |       3 |
| December, 29 2011 00:00:00+0000 |       3 |
| December, 30 2011 00:00:00+0000 |       3 |
| December, 31 2011 00:00:00+0000 |       3 |
|  January, 01 2012 00:00:00+0000 |       3 |
|  January, 02 2012 00:00:00+0000 |       4 |
|  January, 03 2012 00:00:00+0000 |       4 |
|  January, 04 2012 00:00:00+0000 |       4 |
|  January, 05 2012 00:00:00+0000 |       5 |
|  January, 06 2012 00:00:00+0000 |       5 |
|  January, 07 2012 00:00:00+0000 |       5 |
|  January, 08 2012 00:00:00+0000 |       5 |
|  January, 09 2012 00:00:00+0000 |       5 |
|  January, 10 2012 00:00:00+0000 |       5 |
|  January, 11 2012 00:00:00+0000 |       5 |
|  January, 12 2012 00:00:00+0000 |       5 |
|  January, 13 2012 00:00:00+0000 |       5 |
|  January, 14 2012 00:00:00+0000 |       5 |
|  January, 15 2012 00:00:00+0000 |       5 |
|  January, 16 2012 00:00:00+0000 |       5 |
|  January, 17 2012 00:00:00+0000 |       5 |
|  January, 18 2012 00:00:00+0000 |       5 |
|  January, 19 2012 00:00:00+0000 |       5 |
|  January, 20 2012 00:00:00+0000 |       5 |
|  January, 21 2012 00:00:00+0000 |       5 |
|  January, 22 2012 00:00:00+0000 |       5 |
|  January, 23 2012 00:00:00+0000 |       5 |
|  January, 24 2012 00:00:00+0000 |       5 |
|  January, 25 2012 00:00:00+0000 |       5 |
|  January, 26 2012 00:00:00+0000 |       5 |
|  January, 27 2012 00:00:00+0000 |       5 |
|  January, 28 2012 00:00:00+0000 |       5 |
|  January, 29 2012 00:00:00+0000 |       5 |
|  January, 30 2012 00:00:00+0000 |       5 |
|  January, 31 2012 00:00:00+0000 |       5 |
| February, 01 2012 00:00:00+0000 |       5 |
| February, 02 2012 00:00:00+0000 |       5 |
| February, 03 2012 00:00:00+0000 |       5 |
| February, 04 2012 00:00:00+0000 |       5 |
| February, 05 2012 00:00:00+0000 |       5 |
| February, 06 2012 00:00:00+0000 |       5 |
| February, 07 2012 00:00:00+0000 |       5 |
| February, 08 2012 00:00:00+0000 |       5 |
| February, 09 2012 00:00:00+0000 |       5 |
| February, 10 2012 00:00:00+0000 |       6 |
| February, 11 2012 00:00:00+0000 |       6 |
| February, 12 2012 00:00:00+0000 |       6 |
| February, 13 2012 00:00:00+0000 |       6 |
| February, 14 2012 00:00:00+0000 |       6 |
| February, 15 2012 00:00:00+0000 |       6 |
| February, 16 2012 00:00:00+0000 |       6 |
| February, 17 2012 00:00:00+0000 |       6 |
| February, 18 2012 00:00:00+0000 |       6 |
| February, 19 2012 00:00:00+0000 |       6 |

php - 为这个简单的代码减少许多 SQL 查询

3 回答 3

Related

Reference