令人费解的php/mysql时间算术行为 [英] Perplexing php/Mysql Time arithmetic behaviour

问题描述

我正在尝试选择过去90秒钟内输入的所有条目，并针对这样提取的每一行:

I am trying to SELECT all entries entered in last ninety seconds and for each row thus fetched:

• 显示其插入时间与当前时间之间的时差(以diff表示)
• 显示记录要比90秒(待定)还早的剩余秒数

表结构:

attempt_id    |   username   |   attempt_ip   |   attempt_time  

这是我正在使用的查询:

This is the query I am using :

SELECT *, (NOW() - attempt_time) diff, ( 90 + attempt_time - NOW() ) pending, 
NOW() nw FROM failed_login WHERE (username = 'some_username' 
OR attempt_ip = '127.0.0.1') AND NOW() - attempt_time < 90;

但是我得到的结果不一致:

But I am getting inconsistent results:

测试运行

另一个测试运行

完整代码(如果您想尝试):

<?php

date_default_timezone_set('UTC');

function please_monsieur_db($qry) 
{
    $con = mysql_connect("localhost", "root", "");
    if(!$con)
        die("Unable to connect. " . mysql_error());

    $db = mysql_select_db("temp_test");
    if(!$db)
        die("Unable to select database. " . mysql_error());

    $res = mysql_query($qry);
    if(!$res)
        echo "\nQuery failed: $qry" . mysql_error();

    return $res;
}

/* Insert 3 records with a time gap between 2 and 8 sec after each insert */
$k      = 0;
while($k != 3)
{
    $q      = "INSERT INTO failed_login (username, attempt_ip) VALUES ('some_username', '127.0.0.1');";
    $rs     = please_monsieur_db($q);
    if($rs)
        echo "Insert @ " . time() . "\n";
    sleep(rand(2, 8));
    $k++;
}

/*
 * SELECT all attempts in last ninety seconds and for each show the difference
 * between their insertion time and the current time (diff) and 
 * number of seconds left post which the record will be older than 90 secs.
 * Output the status every 2 seconds
 */
$m = 1;
while($m)
{
    $query  = "SELECT *, (NOW() - attempt_time) diff, (90 + attempt_time - NOW()) pending, NOW() nw  FROM failed_login 
            WHERE (username = 'some_username' OR attempt_ip = '127.0.0.1') AND NOW() - attempt_time < 90;";

    $res    = please_monsieur_db($query);

    if(!$res)
        exit;

    $ct     = mysql_num_rows($res);
    echo "\n";
    while($row = mysql_fetch_array($res))
    {
        echo "Now:" . strtotime($row['nw']) . " || Attempt Time: " . strtotime($row['attempt_time']) . 
        " || Diff: [NOW() - attempt_time] = " . $row['diff'] . " || Pending [90-Diff] = : " . $row['pending'] . "\n";
    }
    echo "\n";
    sleep(2);
    $m = $ct;
}
?>

表代码(如果需要):

CREATE DATABASE temp_test;
DROP TABLE IF EXISTS failed_login;

CREATE TABLE failed_login (
   attempt_id      INT AUTO_INCREMENT PRIMARY KEY,
   username        VARCHAR(256),
   attempt_ip      VARCHAR(16),
   attempt_time    TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

注意:要实时输出，请使用命令行运行.

Note: For real time output, run using command line.

$php -f /path_to_script/script.php  

推荐答案

这是因为您正在执行从mysql日期时间到整数的隐式转换.

It's because you're doing an implicit cast from a mysql datetime to an integer.

例如mysql认为时间(如我所写的)是2011-12-15 13:42:10，但是如果我要求mysql从中减去90，它将锻炼20111215134210-90 = 20111215134120这是13:41:20这是50秒前.

E.g. mysql thinks the time (as I write this) is 2011-12-15 13:42:10 but if I asked mysql to subtract 90 from this, it would workout 20111215134210 - 90 = 20111215134120 which is 13:41:20 Which is 50 seconds ago.

要么将时间视为整数(通过转换到/从unix时间戳转换，如liquorvicar所建议)，要么使用date函数对日期值进行数学运算:

Either treat the time as an integer (by converting to/from a unix timestamp, as suggested by liquorvicar) or use the date functions to do maths on a date value:

SELECT *, 
timediff(NOW(), attempt_time) diff, 
timediff(NOW(), attempt_time + INTERVAL 90 SECONDS) pending,
NOW() nw 
FROM failed_login 
WHERE (username = 'some_username' 
     OR attempt_ip = '127.0.0.1') 
AND NOW() - INTERVAL 90 SECONDS > attempt_time;

(请注意，我还重写了最后一个过滤器表达式，使得表列在表达式的一侧被隔离-当未对索引建立索引时，它具有较小的速度优势，而对索引建立索引时则具有巨大的优势)

(note that I've also rewritten the last filter expression such that the table column is isolated on one side of the expression - which has a small speed benefit when the column is nor indexed but a huge beneift when it is indexed).

或者使用秒-自纪元....

Or using seconds-since-epoch....

SELECT *, 
UNIX_TIMESTAMP(NOW()) - UNIX_TIMESTAMP(attempt_time) diff, 
UNIX_TIMESTAMP(NOW()) - UNIX_TIMESTAMP(attempt_time) + 90 pending,
NOW() nw 
FROM failed_login 
WHERE (username = 'some_username' 
     OR attempt_ip = '127.0.0.1') 
AND UNIX_TIMESTAMP(NOW()) - 90 > UNIX_TIMESTAMP(attempt_time);

(显然将无法使用索引优化).

(which obviously won't be able to use index optimization).

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