Question

有两个表格文章和类别。

  nid | title | status
---+-------------+-------
 1 |           abc |     1
 2 |           ggg |      1
 3 |           kkk |      0
 4 |          rrr |      1
 5 |           fff |      1
 6 |           ggg |      1

发布status = 1的地方。

cid | nid 
---+-------------
 1 |           1 
 2 |           2 
 2 |            3 
 3 |           4 
 1 |           5 
 2 |           6

现在我希望为每个cid获得一个nid，而不会出现状态为1的cid双重出现。

Answer 1

您可以使用聚合：

select c.cid, max(c.nid)
from category c join
     article a
     on c.nid = a.nid
where a.status = 1
group by c.cid;

Answer 2

您可以将GROUP BY与JOIN一起使用，例如：

SELECT t2.cid, MAX(t2.nid)
FROM table2 t2 JOIN table1 t1 ON t2.nid = t1.nid and t1.status = 1
GROUP BY t2.cid;

Answer 3

首先，您必须决定在多个匹配的情况下为cid显示哪个nid。假设你想要最大的nid。从类别中选择并查找文章的状态。然后聚合。

select cid, max(nid)
from category
where nid in (select nid from article where status = 1)
group by cid;

Answer 4

试试这个。

SELECT DISTINCT cid 
FROM category       AS a1
INNER JOIN article  AS a2 ON a1.nid = a2.nid
WHERE a1.[STATUS] = 1

SQL：获取每个类别的文章

4 个答案: