[英]Select count from a table with a Where on another table
我有兩張桌子
我需要通過對id_ad進行分組來計算訪問次數,這是可行的,但我還需要在25天前發布前9個結果。
這是我目前的查詢:
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
但是當我嘗試在phpmyadmin中輸入查詢時,它崩潰了。
我究竟做錯了什么?
問題的根源大概是兩個表之間的笛卡爾積。 簡單規則:請勿在from
子句中使用逗號。 始終使用顯式join
語法。
我想象您想要的查詢看起來像這樣:
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;
我想你忘記了解析DATE_SUB(NOW(), INTERVAL 25 DAY)
為DATE
,同時與日期比較。 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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