Question

我收到了以下表格：

pictures
------------------------------------
id
name
views

votes
------------------------------------
id
user_id
pic_id

我想从一个查询中得到一个结果，该查询会给我每个图片ID，图片的视图，以及特定pic_id的表votes的总投票数

示例：

pictures.id，pictures.views，total votes

1 ------------ 78 ------------------ 123

2 ------------ 23 ------------------- 69

依旧......

我试过的代码：

SELECT `pictures`.`id`,`pictures`.`views`, COUNT(`votes`.`pic_id`) as votes
FROM `pictures` 
JOIN `votes`
ON `pictures`.`id` = `votes`.`pic_id`

但它并没有给我我想要的重复。

Answer 1

您需要GROUP BY条款。

使用LEFT JOIN将显示表pictures上的所有记录，无论是否有表votes上的匹配记录。

SELECT  a.id, a.name, a.views,
        COUNT(b.pic_id) TotalVotes
FROM    pictures a
        LEFT JOIN votes b
            ON a.id = b.pic_id
GROUP   BY a.id, a.name, a.views

Answer 2

将左连接与组函数一起使用，普通连接关键字表示内连接，您需要左连接以实现一对多关系

SELECT `pictures`.`id`,`pictures`.`views`, COUNT(`votes`.`pic_id`) as votes
FROM `pictures` 
LEFT JOIN `votes`
ON `pictures`.`id` = `votes`.`pic_id`
GROUP BY `pictures`.`id`

Answer 3

试试这个：

SELECT `pictures`.`id`,`pictures`.`views`, COUNT(`votes`.`pic_id`) as votes
FROM `pictures` 
JOIN `votes`
ON `pictures`.`id` = `votes`.`pic_id`
GROUP BY `votes`.`pic_id`;

Answer 4

您需要使用GROUP BY子句尝试这样做：

SELECT `pictures`.`id`,`pictures`.`views`, COUNT(`votes`.`pic_id`) as votes
FROM `pictures` 
JOIN `votes`
ON `pictures`.`id` = `votes`.`pic_id`
group by `pictures`.`id`

来自另一个表的count（）的SQL查询

4 个答案: