[英]Select count from a table with a Where on another table
我有两张桌子
我需要通过对id_ad进行分组来计算访问次数,这是可行的,但我还需要在25天前发布前9个结果。
这是我目前的查询:
SELECT count(v.id_ad) AS visits,
v.id_ad,
a.published
FROM oc2_visits AS v,
oc2_ads AS a
WHERE DATE(a.published) >= DATE_SUB(NOW(), INTERVAL 25 DAY)
GROUP BY v.id_ad
ORDER BY visits DESC LIMIT 0,9
但是当我尝试在phpmyadmin中输入查询时,它崩溃了。
我究竟做错了什么?
问题的根源大概是两个表之间的笛卡尔积。 简单规则:请勿在from
子句中使用逗号。 始终使用显式join
语法。
我想象您想要的查询看起来像这样:
SELECT count(v.id_ad) AS visits, v.id_ad, a.published
FROM oc2_visits v join
oc2_ads a
ON v.id_ad = a.id_ad
WHERE DATE(a.published) >= DATE_SUB(NOW(), INTERVAL 25 DAY)
GROUP BY v.id_ad
ORDER BY visits DESC
LIMIT 0, 9;
我想你忘记了解析DATE_SUB(NOW(), INTERVAL 25 DAY)
为DATE
,同时与日期比较。 希望它能工作。
SELECT count(v.id_ad) AS visits,
v.id_ad,
a.published
FROM oc2_visits AS v,
oc2_ads AS a
WHERE DATE(a.published) >= DATE(DATE_SUB(NOW(), INTERVAL 25 DAY))
GROUP BY v.id_ad
ORDER BY visits DESC LIMIT 0,9
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