Is subquery the solution to this? - mysql

Question

Here's the table structure and some sample data:
pID.....month.....year
27 .....3 .....2008
27 .....12 .....2012
31 .....6 .....2008
99 .....1 .....2006
42 .....1 .....2009
pID is the practiceID and month and year represent the date period they've entered data for. I need to grab the number of practices that have entered data for the first time in Oct 2012, Nov 2012, Dec 2012 and so on.
I tried the following query for Oct 2012:
SELECT *
FROM
IPIPKDIS
where
practiceID NOT IN (
SELECT practiceID
from
IPIPKDIS
where
year < 2012 and month < 10
)
and year = 2012
and month = 10
and measureCatRecID = 2
ORDER BY year, month;
but it's grabbing months and year less than 10/2012.
If I run the queries isolated (not as subquery) they both work fine.
Any ideas?

Answer 1

This summary query will yield the first (smallest) date in the table for each value of practiceID.
SELECT practiceID,
MIN(STR_TO_DATE( CONCAT(year, ' ', month), '%Y %m')) first_date
FROM IPIPKDIS
GROUP BY practiceID
If you want to retrieve then the whole row for the first reported month, you'd do a nested query like this:
SELECT *
FROM IPIPKDIS I
JOIN (
SELECT practiceID,
MIN(STR_TO_DATE( CONCAT(year, ' ', month), '%Y %m')) first_date
FROM IPIPKDIS
GROUP BY practiceID
) first ON ( first.practiceID = I.practiceID
AND STR_TO_DATE( CONCAT(I.year, ' ', I.month), '%Y %m') = first.first_date)
The trick to the second query is to use the JOIN to extract just the first-month rows from your table. We use date arithmetic to do the date comparisons.