sql-server - 计算表中出现的次数

Question

我想[listings]根据相同的用户 ID 值从 [ads] 表中选择标题列和列表出现的次数。

结果应如下所示：

[title] [cnt]  
Acme    5  
MSFT    10  
GOOG    7  

ETC

这不起作用：

select 
    l.title,
    (COUNT (id) FROM ads WHERE ads.userid = l.userid) as cnt
from 
    listings l
INNER JOIN 
    ads a on a.userid = l.userid
WHERE 
    l.listingtype = 2

Answer 1

我认为查询和其他答案过于复杂

select 
    l.title,
    COUNT (a.id) as cnt
from 
    listings l
INNER JOIN 
    ads a on a.userid = l.userid
WHERE 
    l.listingtype = 2
GROUP BY l.title

Answer 2

您需要一个group by子句来实现它。

像这样的东西： -

select l.title,COUNT (id) 
(SELECT  COUNT (id) FROM ads WHERE ads.userid=l.userid) as cnt
from listings l
INNER JOIN ads a on a.userid=l.userid
WHERE l.listingtype=2
group by l.title

Answer 3

你需要SELECT在你的子查询中：

SELECT
    l.title,
    (SELECT COUNT (id) FROM ads WHERE ads.userid = l.userid) AS cnt
FROM 
    listings l
INNER JOIN 
    ads a on a.userid = l.userid
WHERE 
    l.listingtype = 2