JOIN表中具有MAX（timestamp）的GROUP BY

Question

This is my first post here and already asking for help :/.

I'm really struggling to create this report, I've been learning mySQL for the last couple of months and I need help.

I have 4 tables that have foreign keys and In summary I need to retrieve the value of 2 of those tables where the most recent create date:

table1

ID  created         Date2   Amount   foreignkey1

1   6/14/17 12:08   7/13/17  0      3112602
2   6/14/17 12:08   7/20/17  0      3112602
3   6/14/17 12:08   7/20/17  1000   3112602
4   6/14/17 12:18   7/20/17  3631   3112602
5   6/14/17 13:06   7/20/17  6483   3112602
6   6/2/17 10:06    7/1/17   0      3099667
7   6/2/17 10:06    7/16/17  0      3099667
8   6/30/17 6:54    7/16/17  10163  3099667
9   6/30/17 6:55    7/16/17  10163  3099667

table2

ID  Created        Date3    foreignkey2

1   10/4/11 17:46   NULL    1373280
2   2/6/12 21:10    NULL    1373280
3   11/16/12 20:23  NULL    1373280
4   3/19/13 12:03   NULL    1373280
5   5/27/17 7:48    NULL    1373280
6   5/30/17 13:56   NULL    1373280
7   5/30/17 14:32   7/1/17  1373280
8   6/2/17 8:06     7/16/17 1373280
8   3/19/09 16:34   NULL    1372612
8   1/18/17 18:12   NULL    1372612
8   6/14/17 6:24    7/20/17 1372612

table3

ID  foreignkey1 foreignkey2

1   1372612     3112602
2   1373280     3099667

table4

ID  foreignkey1 country

1   1372612      Mordor
2   1373280      Mordor

What I need is a query that retrieves something like this:

foreignkey1 foreignkey2  date2       date3    country

3112602     1372612      7/20/17     7/20/17   Mordor
3099667     1373280      7/16/17     7/16/17   Mordor

I need to join both foreign keys using table3 and retrieve both date2 and date3 WHERE created is the most recent date on each table.

I tried something like this:

SELECT tb1.foreignkey1, tb2.foreignkey2, tb1.date2, tb2.date3, tb3.country FROM table1 tb1
    LEFT JOIN table3 tb3 on tb1.foreignkey1=tb3.foreignkey1
    LEFT JOIN table2 tb2 on tb2.foreignkey2=tb3.foreingkey2
    LEFT JOIN table4 tb4 on tb2.foreignkey1=tb4.foreingkey4
WHERE tb1.created>"2017-06-01" AND tb4.country="Mordor" AND tb1.created IN (SELECT MAX(ca.created)) AND tb2.created = (SELECT MAX(tb2.created))  AND tb1.date2 >"2017-06-01" AND tb2.date3 >"2017-06-01" GROUP BY cu.ID;

Unfortunately I haven't had success in this mission, I need help :(

Thanks!

Answer 1

Start by getting the data with the max(created) date from each table and then join to that table. For example:

SELECT  foreignkey1 ,
    foreignkey2 ,
    date2 ,
    date3 ,
    country
FROM    ( SELECT    MAX(id) AS id ,
                foreignkey1 ,
                MAX(created) AS created ,
                MAX(date2)
      FROM      table1
      GROUP BY  foreignkey1
    ) t1
    JOIN table3 t3 ON t3.foreignkey1 = t1.foreignkey1
    JOIN ( SELECT   MAX(id) AS id ,
                    foreignkey2 ,
                    MAX(date3) ,
                    MAX(created) AS created
           FROM     table2
           GROUP BY foreignkey2
         ) t2 ON t2.foreignkey2 = t3.foreignkey2
    JOIN table4 t4 ON t4.foreignkey1 = t1.foreignkey1;

I might be off by the joins as I did not recreate the data on my PC, but that's one way to go about it...

Answer 2

Could be you have some problem with on clause

    SELECT 
        tb1.foreignkey1
        , tb2.foreignkey2
        , tb1.date2
        , tb2.date3
        , tb4.country 
    from table1 tb1
    left join table3 tb3 on tb1.foreignkey1=tb3.foreignkey2
    left join table2 tb2 on tb2.foreignkey2=tb3.foreingkey1
    left join table4 tb4 on tb3.foreignkey1=tb4.foreingkey1
    WHERE tb1.created>"2017-06-01" 
    AND tb4.country="Mordor" 
    AND tb1.created IN (SELECT MAX(ca.created)) 
    AND tb2.created = (SELECT MAX(tb2.created))  
    AND tb1.date2 >"2017-06-01" AND tb2.date3 >"2017-06-01" 
    GROUP BY cu.ID;