Question

first off: thanks for looking; your time is appreciated!

to the point:

SCHEMA: for myTable

nonUniqueID    YEAR    MONTH    DAY    HOUR    numericValue
1              2012    01       01     01      99.9
1              2012    01       01     02      65.2
1              2012    01       01     03      -88
7              2012    02       08     21      9.08
1              2012    01       01     09      99.913
1              2013    01       01     01      99.999999

Basically, it’s two values nonUniqueID and numericValue with a granular date.

Now, i need to get the single greatest date in this entire database. With the data above, the expected result would be:

nonUniqueID    YEAR    MONTH    DAY    HOUR    numericValue
1              2013    01       01     01      99.999999

Because this is SQLite, i know that i will end up having to use MAX() several times. The order will have to be MAX(YEAR) then MAX(MONTH) then MAX(DAY) then MAX(HOUR).

Basically, the query would work like this (i just don’t know enough about SQL syntax to create the query):

1. Find all records with highest YEAR
2. From this set, find all records with highest MONTH
3. From this set, find all records with highest DAY
4. From this set, find all records with highest HOUR
5. return this record

Here is a SQL that i adapted from another StackExchange question that does not work

Select * From ( 
    Select max(YEAR) as Y FROM myTable 

    union 

    Select max(MONTH) as M FROM myTable 

    union 

    Select max(DAY) as D FROM myTable 

    union

    Select max(HOUR) as H FROM myTable 
) myTable;

which returns

Y
-----
21 
08 
02 
2013

Compare this to expected out:

nonUniqueID    YEAR    MONTH    DAY    HOUR    numericValue
1              2013    01       01     01      99.999999

it returned 4 records instead of the one record with the 4 values.

Can somebody please help me with my query? THANK YOU!

Answer 1

Try this

 SELECT nonUniqueID ,  YEAR ,  MONTH ,  DAY ,  HOUR ,  numericValue FROM myTable as a
 INNER JOIN (Select max(MONTH) FROM  myTable) as b
 ON a.YEAR = B.YEAR
 INNER JOIN (Select max(DAY) FROM myTable) as c
 ON b.YEAR = c.YEAR
 INNER JOIN (Select max(HOUR) FROM myTable) as d
 ON c.YEAR = d.YEAR
 WHERE a.YEAR = (Select max(YEAR) FROM myTable) 

It returns 4 values because you use UNION
it means that the result are join in one column

EDIT

Ive just updated my answer see if that works Im not quite sure to the performance of this query