Question

我有这个问题：

$score = 10;
SELECT timecode, count(tag) as n_tags, tag
FROM dados
WHERE dados.tag = 'tag1' 
AND dados.filename = 'file.mp4'
AND (timecode >= '-5' AND timecode <= '15')
AND (timecode = '$score')
GROUP BY timecode
ORDER BY count(tag) DESC

但是我想将6行更改为：

AND (timecode = '$score' AND n_tags > 3)

但它似乎不是正确的方法，它不起作用。

有什么想法吗？

Answer 1

从WHERE子句中删除该行并放入HAVING子句。 HAVING子句将查看聚合结果。没有。

SELECT timecode, count(tag) as n_tags, tag
FROM dados
WHERE dados.tag = 'tag1' 
AND dados.filename = 'file.mp4'
AND (timecode >= '-5' AND timecode <= '15')
AND (timecode = '$score')
GROUP BY timecode
HAVING count(tag) > 3
ORDER BY count(tag) DESC

此行是多余的，可以删除：AND（时间码＆gt; ='-5'和时间码＆lt; ='15'）

SELECT timecode, count(tag) as n_tags, tag
FROM dados
WHERE dados.tag = 'tag1' 
AND dados.filename = 'file.mp4'
AND (timecode = '$score')
GROUP BY timecode
HAVING count(tag) > 3
ORDER BY count(tag) DESC

Answer 2

您不能在WHERE子句中使用聚合字段。 count()结果仅在考虑了所有适用行后才可用。但是where过滤是在解析每个单独行时完成的。陈词滥调，但是你试图在他们孵化之前计算你的鸡。

这类事情必须使用HAVING子句完成，该子句与where基本完全相同，但在最终结果发送回客户端之前应用。所以......

SELECT ..., count(tag) as n_tags
...
WHERE (timecode = '$score')

HAVING (n_tags > 3)

MySQL查询 - 获取列值＆＃34;大于...＆＃34;

2 个答案: