SQL Querying Column on Max Date

Question

I apologize if my code is not properly typed. I am trying to query a table that will return the latest bgcheckdate and status report. The table contains additional bgcheckdates and statuses for each record but in my report I only need to see the latest bgcheckdate with its status.

SELECT BG.PEOPLE_ID, MAX(BG.DATE_RUN) AS DATERUN, BG.STATUS
FROM PKS_BGCHECK BG
GROUP BY BG.PEOPLE_ID, BG.status;

When I run the above query, I still see queries with multiple background check dates and statuses.

Whereas when I run without the status, it works fine:

SELECT BG.PEOPLE_ID, MAX(BG.DATE_RUN)
FROM PKS_BGCHECK BG
GROUP BY BG.PEOPLE_ID;

So just wondering if anyone can help me figure out help me query the date run and status and both reflecting the latest date.

Answer 1

The best solution depends on which RDBMS you are using.

Here is one with basic, standard SQL:

SELECT bg.PEOPLE_ID, bg.DATE_RUN, bg.STATUS
FROM  (
   SELECT PEOPLE_ID, MAX(DATE_RUN) AS MAX_DATERUN
   FROM   PKS_BGCHECK
   GROUP  BY PEOPLE_ID
   ) sub
JOIN PKS_BGCHECK bg ON bg.PEOPLE_ID = sub.PEOPLE_ID
                   AND bg.DATE_RUN = sub.MAX_DATERUN;

But you can get multiple rows per PEOPLE_ID if there are ties.

In Oracle , Postgres or SQL Server and others (but not MySQL) you can also use the window function row_number() :

WITH cte AS (
   SELECT PEOPLE_ID, DATE_RUN, STATUS
        , ROW_NUMBER() OVER(PARTITION BY PEOPLE_ID ORDER BY DATE_RUN DESC) AS rn
   FROM   PKS_BGCHECK
   )
SELECT PEOPLE_ID, DATE_RUN, STATUS
FROM   cte
WHERE  rn = 1;

This guarantees 1 row per PEOPLE_ID . Ties are resolved arbitrarily. Add more expressions to ORDER BY to break ties deterministically.

In Postgres, the simplest solution would be with DISTINCT ON .

Details for both in this related answer:

• Select first row in each GROUP BY group?

Answer 2

Selecting the latest row in a time-sensitive set is fairly easy and largely platform independent:

SELECT BG.PEOPLE_ID, BG.DATE_RUN, BG.STATUS
FROM   PKS_BGCHECK BG
WHERE  BG.DATE_RUN =(
        SELECT MAX( DATE_RUN )
        FROM   PKS_BGCHECK
        WHERE  PEOPLE_ID = BG.PEOPLE_ID
          AND  DATE_RUN < SYSDATE );

If the PK is (PEOPLE_ID, DATE_RUN), the query will execute about as quickly as any other method. If they don't form the PK (why not???) then use them to form a unique index. But I'm sure you're already doing one or the other.

Btw, you don't really need the and part of the sub-query if you don't allow future dates to be entered. Some temporal implementations allow for future dates (planned or scheduled events) so I'm used to adding it.