mysql - Grouping in an SQL Query -


this question has answer here:

i have 3 tables schema below:

please check sqlfiddle: http://sqlfiddle.com/#!2/55fc2

table: apps

| id (bigint) | userid (bigint)|      start_time (datetime) |  ------------------------------------------------------------- |  1          |        13     |         2013-05-03 04:42:55 |  |  2          |        13     |         2013-05-12 06:22:45 | |  3          |        13     |         2013-06-12 08:44:24 |     |  4          |        13     |         2013-06-24 04:20:56 |        |  5          |        13     |         2013-06-26 08:20:26 |        |  6          |        13     |         2013-09-12 05:48:27 |

table: hosts

| id (bigint) | appid (bigint)|         device_id (bigint)  |  ------------------------------------------------------------- |  1          |        1      |                           1 |  |  2          |        2      |                           1 | |  3          |        1      |                           1 |     |  4          |        3      |                           3 |        |  5          |        1      |                           4 |       |  6          |        2      |                           3 |

table: usage

| id (bigint) | appid (bigint)|             hostid (bigint) |   factor (varchar)    |   ------------------------------------------------------------------------------------- |  1          |        1      |                           1 |               low     |  |  2          |        1      |                           3 |               high    |  |  3          |        2      |                           2 |               low     |  |  4          |        3      |                           4 |               medium  |  |  5          |        1      |                           5 |               low     |  |  6          |        2      |                           2 |               medium  |

now if put userid, want count of rows of table rows each month (of app) each "factor" month wise last 6 months.

if device_id appears more once in month (based on start_time, based on joining apps , hosts), latest rows of usage (based on combination of apps, hosts , usage) considered calculating count.

example output of query above example should be: (for input user id=13)

| month       | usage_count   |               factor        |  ------------------------------------------------------------- |  5          |        0      |                 high        |  |  6          |        0      |                 high        |  |  7          |        0      |                 high        |  |  8          |        0      |                 high        |        |  9          |        0      |                 high        |        |  10         |        0      |                 high        |  |  5          |        2      |                 low         |  |  6          |        0      |                 low         |  |  7          |        0      |                 low         |  |  8          |        0      |                 low         |        |  9          |        0      |                 low         |        |  10         |        0      |                 low         | |  5          |        1      |                 medium      |  |  6          |        1      |                 medium      |  |  7          |        0      |                 medium      |  |  8          |        0      |                 medium      |        |  9          |        0      |                 medium      |        |  10         |        0      |                 medium      |

how calculated?

  1. for month may 2013 (05-2013), there 2 apps table apps
  2. in table hosts , these apps associated device_id's 1,1,1,4,3
  3. for month (05-2013) device_id=1, latest value of start_time is: 2013-05-12 06:22:45 (from tables hosts,apps), in table usage, combination of appid=2&hostid=2 there 2 rows 1 factor low , other medium,
  4. for month (05-2013) device_id=4, following same procedure 1 entry i.e 0 low
  5. similarly values calculated.

to last 6 months via query i'm trying following:

select month(date_add(now(), interval aint month)) amonth         (         select 0 aint union select -1 union select -2 union select -3 union select -4 union select -5     )

you need understand use of group by. thats looking for. can group results independent groups , use count , aggregation functions on groups independently. here basic tutorial.


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