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MySQL Query Question

Posted on 2007-04-01
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I have a table that stores historical statistics.  I'm using it to query timeline data.

+----------------------+------------+------+-----+---------------------+----------------+
| Field                | Type       | Null | Key | Default             | Extra          |
+----------------------+------------+------+-----+---------------------+----------------+
| id      | bigint(20) | NO   | PRI | NULL                | auto_increment |
| person_id            | bigint(20) | NO   | MUL |                     |                |
| time_hack            | datetime   | NO   |     | 0000-00-00 00:00:00 |                |
| statA       | int(4)     | YES  |     | NULL                |                |
| statB | int(4)     | YES  |     | NULL                |                |
| statC        | int(4)     | YES  |     | NULL                |                |
| statD | int(4)     | YES  |     | NULL                |                |
| statE | int(4)     | YES  |     | NULL                |                |
+----------------------+------------+------+-----+---------------------+----------------+

The query I'm using:

            SELECT * FROM
            `performance_history`
            WHERE
            `performance_history`.`time_hack` >= DATE_SUB(CURRENT_DATE, INTERVAL 30 DAY);

The problem I'm finding multiple records per person per day.  It appears the table records were inputted hourly rather than daily.    So I want to modify my query so I only retrieve one record per person per day.
The following table shows 4 records for person #1 generated on SEP, 15 2006.    Aside from the date, all the data is the same so I only need one of these records for this day.


|              15 |        1 | 2006-09-15 01:46:58 |                        2 |            38 |                   77 |                  100 |
|              16 |        1 | 2006-09-15 02:46:58 |                        2 |            38 |                   77 |                  100 |
|              17 |        1 | 2006-09-15 03:46:58 |                        2 |            38 |                   77 |                  100 |
|              18 |        1 | 2006-09-15 04:46:58 |                        2 |            38 |                   77 |                  100 |              


How do I modify my query so I retrieve only 1 record per person, per day?
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Comment
Question by:tmonteit
6 Comments
 
LVL 27

Assisted Solution

by:Cornelia Yoder
Cornelia Yoder earned 600 total points
ID: 18832658
           SELECT * FROM
            `performance_history`
            WHERE
            `performance_history`.`time_hack` >= DATE_SUB(CURRENT_DATE, INTERVAL 30 DAY) GROUP BY person_id;
0
 

Author Comment

by:tmonteit
ID: 18832994
yodercm,

your recommendation only produces one record per person for the entire 30 day interval.  I need 1 record per day per person for the interval.  

Assume the table has these values.  The result should produce 2 records. One for the 15th, and another for the 16th.

|              15 |        1 | 2006-09-15 01:46:58 |                        2 |            38 |                   77 |                  100 |
|              16 |        1 | 2006-09-15 02:46:58 |                        2 |            38 |                   77 |                  100 |
|              17 |        1 | 2006-09-15 03:46:58 |                        2 |            38 |                   77 |                  100 |
|              18 |        1 | 2006-09-15 04:46:58 |                        2 |            38 |                   77 |                  100 |  
|              19 |        1 | 2006-09-16 01:46:58 |                        3 |            20 |                   74 |                  100 |
|              20 |        1 | 2006-09-16 02:46:58 |                        3 |            20 |                   74 |                  100 |
|              21 |        1 | 2006-09-16 03:46:58 |                        3 |            20 |                   74 |                  100 |
|              22 |        1 | 2006-09-16 04:46:58 |                        3 |            20 |                   74 |                  100 |  


How do I do that?

0
 
LVL 35

Accepted Solution

by:
Raynard7 earned 1400 total points
ID: 18833276
If you did,

SELECT ph.person_id, date(ph.`time_hack`), min(ph.id) mi
FROM
            `performance_history` ph
WHERE
            ph.`time_hack` >= DATE_SUB(CURRENT_DATE, INTERVAL 30 DAY)
GROUP BY
            1, 2

it would give you the ids that you are after, if you did

select
     ph1.*
from
(
            SELECT ph.person_id, date(ph.`time_hack`), min(ph.id) mi
            FROM `performance_history` ph
            WHERE ph.`time_hack` >= DATE_SUB(CURRENT_DATE, INTERVAL 30 DAY)
            GROUP BY 1,2
) x1 inner join `performance_history` ph1 on x1.mi = ph1.id

it would give you all the information, 1 per person per day
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Author Comment

by:tmonteit
ID: 18834111
Raynard, can you explain that more?  MySql Beginner here... is there another table I'm supposed to create?
0
 
LVL 1

Expert Comment

by:krisgrp
ID: 18834462
Hi,
I think u can use the group by cluase to get the resultant u want..
like this.
  SELECT person_id, date(`time_hack`)
            FROM `performance_history`
            WHERE `time_hack` >= DATE_SUB(CURRENT_DATE, INTERVAL 30 DAY)
            GROUP BY person_id,`time_hack` order by id`;
0
 
LVL 35

Expert Comment

by:Raynard7
ID: 18839758
hi, mine should be sufficient

they are all referring to the same table - just doing sub queries on it, (meaning a query within a query) and aliasing (calling a query by an easier to refer to name)

krisgrp - as you will notice that this is what my first query does, however this will not show all the records that the author wants to see - it will only show you the date and the person_id - if you want more you need an id corresponding to one of those records (using a min for example) then linking back onto the same table to pull the rows with that given id
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