1st Row in Group By vs. Last Row

Question

Wondering how to return the 1st row in a MySQL group by vs. the last row. Returning a series of dates, but need the first one displayed.

select * from calendar w         


        

Answer 1

When you use GROUP BY like that, MySQL makes no guarantees about which row in each group you get. Indeed, theoretically it could even pick some of the columns from one row and some from another. The MySQL Reference Manual says:

"MySQL extends the use of GROUP BY so that the select list can refer to nonaggregated columns not named in the GROUP BY clause. [...] You can use this feature to get better performance by avoiding unnecessary column sorting and grouping. However, this is useful primarily when all values in each nonaggregated column not named in the GROUP BY are the same for each group. The server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate."

What you want to do instead is something like this:

SELECT
  calendar.*
FROM
  calendar
  NATURAL JOIN (
    SELECT
      eventid, MIN(date) AS date
    FROM
      calendar
    GROUP BY eventid
  ) AS foo