我一直在使用下面的php和sql来加载英国旅客列车的时刻表信息和实时信息。基本上你必须找到相关的时间表，然后加载每个时间表的实时信息，这些时间表与今天的列车有关。
查询花了比实际想法更长的时间并使用大量的CPU％，这也不是理想的。在sql编程方面我很弱，所以任何关于效率低下的指针都会很棒。
这是一个Android应用程序，所以我试图通过一个呼叫通过http。印刷品（*）和＆gt;用于在另一端分割字符串。
以下是代码：
<?
//Connect to the database
mysql_connect("localhost","XXXX","XXXX")
or die ("No connection could be made to the OpenRail Database");
mysql_select_db("autotrain");
//Set todays date from system and get HTTP parameters for the station,time to find trains and todays locations table.
$date = date('Y-m-d');
$test = $_GET['station'];
$time = $_GET['time'];
$table = $_GET['table'];
//Find the tiploc associated with the station being searched.
$tiplocQuery = "SELECT tiploc_code FROM allstations WHERE c LIKE '$test';";
$tiplocResult =mysql_query($tiplocQuery);
$tiplocRow = mysql_fetch_assoc($tiplocResult);
$tiploc=$tiplocRow['tiploc_code'];
//Now find the timetabled trains for the station where there exists no departure information. Goes back two hours to account for any late running.
$timeTableQuery = "SELECT tiplocs.tps_description AS 'C', locations$table.public_departure, locations$table.id,schedules.stp_indicator
,schedules.train_uid
FROM locations$table, tiplocs, schedules_cache, schedules,activations
WHERE locations$table.id = schedules_cache.id
AND schedules_cache.id = schedules.id
AND schedules.id =activations.id
AND '$date'
BETWEEN schedules.date_from
AND schedules.date_to
AND locations$table.tiploc_code = '$tiploc'
AND locations$table.real_departure LIKE '0'
AND locations$table.public_departure NOT LIKE '0'
AND locations$table.public_departure >='$time'-300
AND locations$table.public_departure <='$time'+300
AND schedules.runs_th LIKE '1'
AND schedules_cache.destination = tiplocs.tiploc
ORDER BY locations$table.public_departure ASC
LIMIT 0,30;";
$timeTableResult=mysql_query($timeTableQuery);
while($timeTablerow = mysql_fetch_assoc($timeTableResult)){
$output[] = $timeTablerow;
}
//Now for each id returned in the timetable, get the locations and departure times so the app may calculate expected arrival times.
foreach ($output as $value) {
$id = $value['id'];
$realTimeQuery ="SELECT locations$table.id,locations$table.location_order,locations$table.arrival,locations$table.public_arrival,
locations$table.real_arrival,locations$table.pass,locations$table.departure,locations$ table.public_departure,locations$table.real_departure,locations$table.location_cancelled,
tiplocs.tps_description FROM locations$table,tiplocs WHERE id =$id AND locations$table.tiploc_code=tiplocs.tiploc;";
$realTimeResult =mysql_query($realTimeQuery);
while($row3 = mysql_fetch_assoc($realTimeResult)){
$output3[] = $row3;
}
print json_encode($output3);
print("*");
unset($output3);
unset($id);
}
print('>');
print json_encode($output);
?>
非常感谢 马特
答案 0 :(得分：0)
我注意到的一些事情。
首先，您将在where子句中加入表，如此
from table1, table2
where table1.something - table2.something
加入from子句更快
from table1 join table2 on table1.something - table2.something
接下来，我不是一个php程序员，但看起来你在循环中运行类似的查询。如果这是真的，那就找一种只运行一个查询的方法。
编辑从此处开始
这是对gazarsgo的回应，我通过声称关于where子句中的连接速度更快来支持。他是对的，我错了。这就是我做的。编程语言是ColdFusion：
<cfsetting showdebugoutput="no">
<cfscript>
fromtimes = ArrayNew(1);
wheretimes = ArrayNew(1);
</cfscript>
<cfloop from="1" to="1000" index="idx">
<cfquery datasource="burns" name="fromclause" result="fromresult">
select count(distinct hscnumber)
from burns_patient p join burns_case c on p.patientid = c.patientid
</cfquery>
<cfset ArrayAppend(fromtimes, fromresult.executiontime)>
<cfquery datasource="burns" name="whereclause" result="whereresult">
select count(distinct hscnumber)
from burns_patient p, burns_case c
where p.patientid = c.patientid
</cfquery>
<cfset ArrayAppend(wheretimes, whereresult.executiontime)>
</cfloop>
<cfdump var="#ArrayAvg(fromtimes)#" metainfo="no" label="from">
<cfdump var="#ArrayAvg(wheretimes)#" metainfo="no" label="where">
我确实跑了5次。结果以毫秒为单位。
9.563 9.611
9.498 9.584
9.625 9.548
9.831 9.769
9.792 9.813
第一个数字表示加入from子句，第二个加入where子句。第一个数字仅在60％的时间内降低。如果它在100％的百分比下降，它会表明加入from子句更快，但事实并非如此。
答案 1 :(得分：0)
您的设置最大的问题是这个foreach循环，因为它是不必要的，导致数次往返数据库以执行查询，获取和分析结果。
foreach ($output as $value) {
重写初始查询以包含稍后计算所需的所有字段。
这样的事情会起作用。
SELECT tl.tps_description AS 'C', lc.public_departure, lc.id, s.stp_indicator, s.train_uid,
lc.id, lc.location_order, lc.arrival, lc.public_arrival, lc.real_arrival, lc.pass, lc.departure, lc.real_departure, lc.location_cancelled
FROM locations$table lc INNER JOIN schedules_cache sc ON lc.id = sc.id
INNER JOIN schedules s ON s.id = sc.id
INNER JOIN activations a ON s.id = a.id
INNER JOIN tiplocs tl ON sc.destination = tl.tiploc
WHERE '$date' BETWEEN schedules.date_from AND schedules.date_to
AND lc.tiploc_code = '$tiploc'
AND lc.real_departure LIKE '0'
AND lc.public_departure NOT LIKE '0'
AND lc.public_departure >='$time'-300
AND lc.public_departure <='$time'+300
AND s.runs_th LIKE '1'
ORDER BY lc.public_departure ASC
LIMIT 0,30;
从页面加载中消除n个查询执行应该会大大增加响应时间。
答案 2 :(得分：0)
忽略代码问题，为了加快查询速度，请使用EXPLAIN命令评估在查询中添加索引的位置。
猜测一下，您可能希望在locations$table.public_departure评估的任何内容上创建索引。