MySQL, getting rows from table with latest date from 2 different columns

Question

I have a mysql db where I import data every morning from an oracle db. The table is about 30million records. This takes about 5-6 hours. At night then I duplicate the table so I can access it from a website that shows a grid with the table content.

the table looks like this

id     userID     fieldID    date1    date2
1         1           1       2014     2014
2         1           1       2014     2016
3         1           1       2013     2017
4         1           2       2014     2016
5         2           3       2014     2016

Basically on the website the user inputs userID and I have to show the records of each fieldID that have the latest date1, and then the latest date2 so the output for userID=1 should be:

id     userID     fieldID    date1    date2
2         1           1       2014     2016
4         1           2       2014     2016

The query I'm using so far is this:

SELECT id,UserID,fieldID,date1,date2 FROM mytable WHERE id = 
( SELECT id from mytable AS lookup 
  WHERE lookup.fieldID = mytable.fieldID
  ORDER BY date1 DESC, date2 DESC
  LIMIT 1 ) AND UserID=1

This works but it takes too long to query the server and load the page, while if I select everything for a specific userID it takes just a second to fetch around 2000 rows

I was wondering if you could suggest a better query or maybe a workaround where instead of duplicating the table, I create the new one with just the records I need (the website isn't used at night).

thanks

Answer 1

SELECT
id,
UserID,
fieldID,
(SELECT MAX(date1) FROM mytable WHERE fieldID=mt.fieldID) As DateOne,
(SELECT MAX(date2) FROM mytable WHERE fieldID=mt.fieldID) As DateTwo,  
FROM mytable mt 
WHERE UserID=1

Answer 2

How about something like:

SELECT  id, mytable.UserID, mytable.fieldID, A.date1, B.date2
FROM    mytable AS outer,
(
    SELECT      MAX(date1) AS date1
    FROM        mytable AS innerone
    WHERE       innerone.id=outer.id
    WHERE       innerone.UserID=outer.UserID
    AND         innerone.fieldID=outer.fieldID
    GROUP BY    innerone.id,
                innerone.UserID,
                innerone.fieldID
)       AS A,
(
    SELECT      MAX(date2) AS date2
    FROM        mytable AS innertwo
    WHERE       innertwo.id=outer.id
    WHERE       innertwo.UserID=outer.UserID
    AND         innertwo.fieldID=outer.fieldID
    GROUP BY    innertwo.id,
                innertwo.UserID,
                innertwo.fieldID
)       AS B
WHERE UserID=1