MYSQL：选择更改的行答案

【问题标题】：MYSQL: Select changed row whereMYSQL：选择更改的行
【发布时间】：2013-06-13 08:14:54
【问题描述】：

1 -

create table changes(snapdate date,value int, uid int); 
insert into changes values 
('2013-04-22', 0, 1 ), 
('2013-04-21', 1,1 ), 
('2013-04-20', 1,1 ), 
('2013-04-19', 1,1 ), 
('2013-04-19', 0,2 ), 
('2013-04-19', 1,1 ), 
('2013-04-18', 0,1 ), 
('2013-04-17', 0,1 ), 
('2013-04-17', 1,2 ), 
('2013-04-16', 1,1 ), 
('2013-04-16', 0 ,2);

2 -

SELECT a.snapdate, a.value 
FROM ( 
  SELECT t1.*, COUNT(*) AS rank 
  FROM changes t1
  LEFT JOIN changes t2 ON t1.snapdate >= t2.snapdate 
  GROUP BY t1.snapdate 
) AS a 
LEFT JOIN ( 
  SELECT t1.*, COUNT(*) AS rank 
  FROM changes t1
  LEFT JOIN changes t2 ON t1.snapdate >= t2.snapdate 
  GROUP BY t1.snapdate 
) AS b ON a.rank = b.rank+1 AND a.value = b.value 
WHERE b.snapdate IS NULL
ORDER BY a.snapdate DESC;

工作正常，但如何选择 WHERE uid=2 例如？我不能使用临时表：

 create temporary table changes_temp
    as
    select *
    from changes
    where uid = 2

http://dev.mysql.com/doc/refman/5.0/en/temporary-table-problems.html

【问题讨论】：

标签： mysql sql

【解决方案1】：

尝试在子查询中添加 WHERE 子句

    SELECT a.snapdate, a.value 
FROM ( 
  SELECT t1.*, COUNT(*) AS rank 
  FROM changes t1
  LEFT JOIN changes t2 ON t1.snapdate >= t2.snapdate 
  WHERE t2.uid=t1.uid AND t2.uid=2
  GROUP BY t1.snapdate 
) AS a 
LEFT JOIN ( 
  SELECT t1.*, COUNT(*) AS rank 
  FROM changes t1
  LEFT JOIN changes t2 ON t1.snapdate >= t2.snapdate 
  WHERE t2.uid=t1.uid AND t2.uid=2
  GROUP BY t1.snapdate 
) AS b ON a.rank = b.rank+1 AND a.value = b.value 
WHERE b.snapdate IS NULL
ORDER BY a.snapdate DESC;

创建SQLFiddle 用于测试。那是你要的吗？您没有解释查询的目标

【讨论】：

【解决方案2】：

添加 where 子句：

SELECT a.snapdate, a.value 
FROM ( 
  SELECT t1.*, COUNT(*) AS rank 
  FROM changes t1
  LEFT JOIN changes t2 ON t1.snapdate >= t2.snapdate 
  WHERE t1.uid = 2
  GROUP BY t1.snapdate 
) AS a 
LEFT JOIN ( 
  SELECT t1.*, COUNT(*) AS rank 
  FROM changes t1
  LEFT JOIN changes t2 ON t1.snapdate >= t2.snapdate 
  WHERE t1.uid = 2
  GROUP BY t1.snapdate 
) AS b ON a.rank = b.rank+1 AND a.value = b.value 
WHERE b.snapdate IS NULL
ORDER BY a.snapdate DESC;

sqlfiddle

【讨论】：