MySQL选择昨天的日期 [英] MySQL selecting yesterday's date

问题描述

如何显示和计算日期为昨天的值? 我使用time()在数据库中插入日期.示例:

How can I display and count the values whose dates are yesterday? I used time() to insert date in the database. Example:

URL: google.com youtube.com google.com youtube.com test.com youtube.com
DateVisited: 1313668492 1313668540 1313668571 13154314

我想显示表中存在多少个具有多个URL的URL，以及昨天已经访问了多少个URL.结果示例:

I want do display how many URLs that have multiple existed in the table and also how many of that URL have been visited yesterday. Example result:

LINK       | timesExisted | timesVisitedYesterday
Google.com |       2      | 2
youtube.com|       3      | 3

我已经有了获取昨天日期的想法，但是我没有一个想法来计算昨天存在一个URL的次数并计算表中存在URL的次数.

I already have the idea on getting yesterday's date, but I don't have an idea on counting how many times a URL has existed for yesterday and counting how many times a URL has existed in the table.

推荐答案

获取昨天日期的最简单，最好的方法是:

The simplest and best way to get yesterday's date is:

subdate(current_date, 1)

您的查询将是:

SELECT 
    url as LINK,
    count(*) as timesExisted,
    sum(DateVisited between UNIX_TIMESTAMP(subdate(current_date, 1)) and
        UNIX_TIMESTAMP(current_date)) as timesVisitedYesterday
FROM mytable
GROUP BY 1

出于好奇，sum(condition)为您提供满足条件的行的 count 的原因(否则需要笨拙且冗长的case语句)是因为在mysql布尔值中1为true，0为false，因此对条件求和有效地算出其为真的次数.使用此模式可以整理您的SQL代码.

For the curious, the reason that sum(condition) gives you the count of rows that satisfy the condition, which would otherwise require a cumbersome and wordy case statement, is that in mysql boolean values are 1 for true and 0 for false, so summing a condition effectively counts how many times it's true. Using this pattern can neaten up your SQL code.

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