Question

我想结束一组数据，以最新的时间戳显示用户。这是我的SQL

SELECT
t2.unit AS UnitNo,
t1.lname AS Name,
t4.code_id AS ActivityNo,
t5.activity_id AS Active,
t4.call_no AS CallNo,
t4.acn_id AS CallStatusNo,
t2.unit_id AS UnitId,
Max(t5.created) created
FROM user AS t1

Inner Join unit AS t2 ON t1.user_id = t2.user_id
Left Join dispatch AS t3 ON t2.unit_id = t3.unit_id
Left Join incident AS t4 ON t4.incident_id = t3.incident_id
Left Join unit_log AS t5 ON t2.unit_id = t5.unit_id
WHERE

t1.id = 1
GROUP BY
t2.unit,
t1.lname,
t4.code_id,
t5.activity_id,
t4.call_no,
t4.acn_id,
t2.unit_id
ORDER BY created desc

我已经附上一张照片来展示我的目标。我最终应该得到的是2排。目前该系统上有2个用户，因此每个用户只能看到一个MAX（已创建）行。即使在分组之后，我也无法理解你所看到的内容。

Answer 1

如果您想要一行，则必须选择要显示的单位ID和活动ID。您正在使用一对多联接，因此您的行当然会成倍增加。

您需要按用户和时间戳对行进行排名。尝试以下（只需替换所有列行）

 SELECT *
    FROM (
    SELECT 
@rn:=if(@prv=product_id, @rn+1, 1) AS rId, 
@prv:=user_id AS user_id, 
ALL your other columns,
timestamp                                                                               
    FROM
      (SELECT t2.unit AS UnitNo,
              t1.lname AS Name,
              t4.code_id AS ActivityNo,
              t5.activity_id AS Active,
              t4.call_no AS CallNo,
              t4.acn_id AS CallStatusNo,
              t2.unit_id AS UnitId,
              Max(t5.created) created
       FROM USER AS t1
       INNER JOIN unit AS t2 ON t1.user_id = t2.user_id
       LEFT JOIN DISPATCH AS t3 ON t2.unit_id = t3.unit_id
       LEFT JOIN incident AS t4 ON t4.incident_id = t3.incident_id
       LEFT JOIN unit_log AS t5 ON t2.unit_id = t5.unit_id
       INNER JOIN
         (SELECT unit_id
          FROM unit_log
          WHERE t1.id = 1
          GROUP BY t2.unit,
                   t1.lname,
                   t4.code_id,
                   t5.activity_id,
                   t4.call_no,
                   t4.acn_id,
                   t2.unit_id
          ORDER BY created DESC ) b
       JOIN
         (SELECT @prv:=0, @rn:=0)tmp
       ORDER BY user_id,
                TIMESTAMP DESC) a
    WHERE rid<=1

如何在数据库中折叠这些行？

1 个答案: