Question

我正在尝试使用下面的查询计算特定字段的记录数。

SELECT COUNT(DISTINCT CASE WHEN seen='n' and reciever_id=1 THEN 'varb' ELSE  'novarb' END) AS count ,c.id, c.vmsg, c.sender_id, p.fname, p.lname, p.profile_pix, p.profile_id
FROM chats c LEFT JOIN profile p  ON c.sender_id = p.profile_id
WHERE c.reciever_id = 1 AND c.id in (SELECT MAX(c.id) as id FROM  chats c
GROUP BY c.sender_id )

但我得到的答案只返回一条记录，而其他数百条显示

Answer 1

如果您使用varb和novarb，如果您有1表示您只有一个条件，那么该数字最多为2

可能需要计算varb条目的数量

SELECT COUNT(
            CASE WHEN seen ='n' and reciever_id=1 
                    THEN 'varb' 
                    ELSE  NULL
            END) AS count ,c.id, c.vmsg, c.sender_id, p.fname, p.lname, p.profile_pix, p.profile_id
FROM chats c 
LEFT JOIN profile p  ON c.sender_id = p.profile_id
WHERE c.reciever_id = 1 AND c.id in (
      SELECT MAX(c.id) as id FROM  chats c
      GROUP BY c.sender_id )

Answer 2

我通常会将SUM()用于此目的。如果我理解正确，您需要满足条件且不符合条件的行数：

SELECT SUM( seen = 'n' and reciever_id = 1 ) as varb,
       SUM( not (seen = 'n' and reciever_id = 1) ) as novarb,
       c.id, c.vmsg, c.sender_id, p.fname, p.lname, p.profile_pix, p.profile_id
FROM chats c JOIN  -- I doubt a left join is necessary
     profile p
     ON c.sender_id = p.profile_id
WHERE c.reciever_id = 1 AND
      c.id in (SELECT MAX(c2.id) FROM  chats c2 GROUP BY c2.sender_id)

计算嵌套查询中的特定行

2 个答案: