Question

I have two MySQL tables and would like to select the highest value results from table2 and append these to table 1.

Table 1 contains ID, MSISDN (14 digit number)

Table 2 contains ID, MSISDN, field2, date

I want to return a list of all MSISDNs in table 1 and also the result for table2.field2 and table2.date where table2.date is the maximum value for the matching MSISDN.

How would I do this? I know I need to use MAX but I’m not sure how to construct the subquery to add the correct result for table2.field.

Answer 1

Typically, you would do this by

• Creating a subselect containing the maximum date for each id
• Joining this subselect with your original table to return the additional columns

Note that if there are two identical (MSISDN, date) records, they will both be returned.

SQL Server

SELECT  t1.MSISDN
        , t2.field2
        , t2.date
FROM    Table1 AS t1
        INNER JOIN Table2 AS t2 ON t2.MSISDN = t1.MSISDN
        INNER JOIN (
          SELECT  MAX(date) AS date, MSISDN
          FROM    Table2
          GROUP BY
                  MSISDN
        ) t2max ON t2max.MSISDN = t2.MSISDN
                   AND t2max.date = t2.date