問(wèn)題描述

表里有個(gè)字段紀(jì)錄每次點(diǎn)擊的時(shí)間，查最近7天每日的數(shù)據(jù)，但其中可能有幾天沒(méi)數(shù)據(jù)，怎么把沒(méi)數(shù)據(jù)的天數(shù)設(shè)置為0，sql語(yǔ)句怎么寫(xiě)

問(wèn)題解答

據(jù)我所知，mysql只能說(shuō)在null的時(shí)候返回其他值（比如SELECT IFNULL( (SELECT field1 FROM table WHERE id = 123) , 0);)，但像題主這樣要補(bǔ)上本來(lái)不存在的數(shù)據(jù)挺難，可能別人會(huì)有方法。

我想說(shuō)的是，就算sql能搞定這件事，也最好不要放sql，而是放在你的應(yīng)用程序里。這種邏輯性的東西放程序里更好管控，也更方便理解

先構(gòu)建一個(gè)最近7天的結(jié)果集，然后和查詢(xún)出的結(jié)果集做Left Join，如：

select a.click_date, ifnull(b.click_qty, 0)from ( select * from ( SELECT curdate() as click_date union all SELECT date_sub(curdate(), interval 1 day) as click_date union all SELECT date_sub(curdate(), interval 2 day) as click_date union all SELECT date_sub(curdate(), interval 3 day) as click_date union all SELECT date_sub(curdate(), interval 4 day) as click_date union all SELECT date_sub(curdate(), interval 5 day) as click_date union all SELECT date_sub(curdate(), interval 6 day) as click_date )) a left join ( select click_date, count(*) as click_qty from click_log_table group by click_date) b