Question

如果你的表格通过FK与其他2个人有关系，是否可以查询主表，同时只计算其ID中存在的ID的次数？

例如：

    id  title    product_id  contact_id
------  -------  ----------  ----------
    11  Mug             110          33
    11  Mug             110         297
    11  Mug             378          33
    11  Mug             378         297
    12  Monster         299          75
    12  Monster         299         291
    12  Monster         299         296

我的查询结果如上：

SELECT t1.id, t1.title, t2.product_id, t3.contact_id FROM t1
    JOIN t2 ON t1.id = t2.rfq_id
    JOIN t3 ON t1.id = t3.rfq_id

我只对COUNT()：

感兴趣

    id  title    product_count  contact_count
------  -------  -------------  -------------
    11  Mug                  2              2
    12  Monster              1              3

Answer 1

您可以尝试使用group by和count distinct个值：

select t1.id
     , t1.title
     , count(distinct t2.product_id) as product_count 
     , count(distinct t3.contact_id) as contact_count
from t1
join t2 on t1.id = t2.rfq_id
join t3 on t1.id = t3.rfq_id
group by t1.id
       , t1.title

Answer 2

试试这些

  SELECT t1.id, t1.title, 
         count(distinct t2.product_id) as product_id, 
         count(distinct  t3.contact_id) as contact_id FROM t1
  JOIN t2 ON t1.id = t2.rfq_id
  JOIN t3 ON t1.id = t3.rfq_id
  group by t1.id, t1.title

谢谢。

Answer 3

您可以执行以下操作：

SELECT t1.id, t1.title, 
       COUNT(DISTINCT t2.product_id) AS product_count, 
       COUNT(DISTINCT t3.contact_id) AS contract_count 
FROM t1
JOIN t2 ON t1.id = t2.rfq_id
JOIN t3 ON t1.id = t3.rfq_id
GROUP BY t1.id, t1.title

MySQL连接在计算连接表时

3 个答案: