SQL：对行进行计数和分组答案

【问题标题】：SQL: Counting and grouping rowsSQL：对行进行计数和分组
【发布时间】：2013-10-04 00:09:17
【问题描述】：

id | userid | exerciseid | date                | time | weight | distance | reps
1  | 24     | 1          | 2013-09-28 00:00:00 | 2321 | 231    | 121      | NULL
2  | 24     | 24         | 2013-09-28 00:00:00 | 2321 | 231    | 121      | NULL
3  | 24     | 1          | 2013-09-28 00:00:00 | 2321 | 231    | 121      | NULL
4  | 24     | 1          | 2000-00-00 00:00:00 | NULL | 100    | NULL     | 2
5  | 24     | 1          | 2013-09-28 00:00:00 | 2321 | 231    | 121      | NULL

第 1、3 和 5 行相同。我想做一个计数，将它们组合在一起，同时添加一个包含计数值的列。

SELECT id, userid, exerciseid, date, time, weight, distance, reps    
FROM `exercises`
WHERE `userid` = 1 AND `date` < now()

所以我希望它也能返回类似的东西：

id | userid | exerciseid | date                | time | weight | distance | reps | count
1  | 24     | 1          | 2013-09-28 00:00:00 | 2321 | 231    | 121      | NULL | 3
4  | 24     | 1          | 2000-00-00 00:00:00 | NULL | 100    | NULL     | 2    | NULL

【问题讨论】：

标签： mysql sql count

【解决方案1】：

试试这个

SELECT id, userid, exerciseid, date, time, weight, distance, reps,
       count(*) as count
FROM `exercises`
WHERE userid = 1 AND date < now()
GROUP BY id, userid, exerciseid, date, time, weight, distance, reps

【讨论】：

如果为 1，count 列是否可以为 NULL？
您可以将 count( * ) 替换为 IF (COUNT( * ) = 1, NULL, COUNT( * )) AS count

【解决方案2】：

试试这个：

SELECT Count(*) As CountM, id, userid, exerciseid, date, time, weight, distance, reps    
FROM `exercises`
WHERE `userid` = 1 AND `date` < now()
Group by id, userid, exerciseid, date, time, weight, distance, reps

【讨论】：