MySQL查询的数量，按分组

Question

Table: statistics

id | user  | Message
----------------------
1  | user1  |message1 
2  | user2  |message2
3  | user1  |message3

I am able to find the count of messages sent by each user using this query.

select user, count(*) from statistics group by user;

How to show message column data along with the count? For example

user | count | message
------------------------
user1| 2     |message1
             |message3
user2| 1     |message2    

Answer 1

You seem to want to show Count by user , which message sent by user .

If your mysql version didn't support window functions, you can do subquery to make row_number in select subquery, then only display rn=1 users and count

CREATE TABLE T(
   id INT,
    user VARCHAR(50),
  Message VARCHAR(100)
);


INSERT INTO T VALUES(1,'user1'  ,'message1'); 
INSERT INTO T VALUES(2,'user2'  ,'message2');
INSERT INTO T VALUES(3,'user1'  ,'message3');

Query 1 :

SELECT (case when rn = 1 then user else '' end) 'users',
       (case when rn = 1 then cnt else '' end) 'count',
       message
FROM (
  select 
      t1.user, 
      t2.cnt, 
      t1.message,
      (SELECT COUNT(*) from t tt WHERE tt.user = t1.user and t1.id >= tt.id) rn
  from T t1
  join (
    select user, count(*) cnt
    from T
    group by user
  ) t2 on t1.user = t2.user
) t1
order by user,message

Results :

| users | count |  message |
|-------|-------|----------|
| user1 |     2 | message1 |
|       |       | message3 |
| user2 |     1 | message2 |

Answer 2

You could join the result of your group by with the full table (or vice versa)?

Or, depending on what you want, you could use group_concat() using \\n as separator.

Answer 3

select user, count(*) as 'total' , group_concat(message) from statistics group by user;

Answer 4

Use Group_concat

select user, count(0) as ct,group_concat(Message) from statistics group by user;

This will give you message in csv format

NOTE: GROUP_CONCAT has size limit of 1024 characters by default in mysql.

For UTF it goes to 1024/3 and utfmb4 255(1024/4).

You can use group_concat_max_len global variable to set its max length as per need but take into account memory considerations on production environment

SET group_concat_max_len=100000000

Update:

You can use any separator in group_concat

Group_concat(Message SEPARATOR '----')

Answer 5

Try grouping with self-join:

select s1.user, s2.cnt, s1.message
from statistics s1
join (
  select user, count(*) cnt
  from statistics
  group by user
) s2 on s1.user = s2.user