Doing a calculation between two rows with EXTRA CRITERIA?

Name      ExactDate  Presents      Location
bob1         2011        1          home
bob2         2008        2          school     
bob2         2012        3          school
mary2        1986        4          school       
mary1        2001        5          home
mary1        2012        6          home    
kate1        2011        7          home
kate1        2012        8          home
kate2        2011        9          school 
celia2       2011       10          school 
celia2       1986       11          school  
celia1       1972       12          home
celia1       2012       14          home 
celia2       2012       13          school

This problem is done in SQL in MS Access 2003 for a query.

So the goal is we subtract the amount of presents kate got from celia on the same year ( b开发者_开发百科ut since there are a few different present values for the same year we choose to have priority of home > school....for example celia and kate both receive presents in 2012 but celia gets both home presents and school presents in 2012 in which case we choose her home present value to do the calculation) and out put should be something like the following:

Name              ExactDate        PresentsDiff
celiaminuskate     2011                      3
celiaminuskate     2012                      6

So far I have :

SELECT 'celiaminuskate'AS [NAME],T1.[date] AS [EXACT DATE],
T1.presents T2.presents AS [PRESENTS DIFF]
FROM Some_Table T1, Some_Table T2 

part that I think needs to be fixed??

WHERE (T1.Name = 'celia1'>'celia2')
AND (T2.Name = 'kate1'>'kate2')
AND T2.ExactDate = T1.ExactDate 

to indicate priority? I'm not too sure how to do it

ORDER BY T1.ExactDate

I created this query and saved it as qryCeliaAndKateGiftDates. It just returns the distinct ExactDate values for which celia and kate both had gifts recorded.

Notice I re-named your Name field to Recipient, because Name is a reserved word.

SELECT DISTINCT celia.ExactDate
FROM
    [SELECT ExactDate
    FROM Some_Table
    WHERE Recipient Like "celia*"
    ]. AS celia
    INNER JOIN [
        SELECT ExactDate
        FROM Some_Table
        WHERE Recipient Like "kate*"
        ]. AS kate
    ON celia.ExactDate = kate.ExactDate
ORDER BY celia.ExactDate;

Then I used correlated subqueries to return the correct Presents values for celia and kate on each of those ExactDates.

SELECT
    raw.recipients AS [NAME],
    raw.ExactDate  AS [EXACT DATE],
    (raw.celia_presents - raw.kate_presents) AS [PRESENTS DIFF]
FROM
    [SELECT
    'celiaminuskate' AS recipients,
    dates.ExactDate,
    (SELECT TOP 1 Presents
    FROM Some_Table
    WHERE
        Recipient Like "celia*"
        And ExactDate = dates.ExactDate
    ORDER BY Location) AS celia_presents,
    (SELECT TOP 1 Presents
    FROM Some_Table
    WHERE
        Recipient Like "kate*"
        And ExactDate = dates.ExactDate
    ORDER BY Location) AS kate_presents
    FROM qryCeliaAndKateGiftDates AS dates]. AS raw;

It returns the results you requested when run from Access 2003. However correlated subqueries are notoriously slow, so I'll be interested to see what other answers you get.