Question

I’m having trouble getting MySQL to return a query properly.

Here’s my data:

id            date            value
2             2011-01-04         55.66
2             2011-03-23         22.33
2             2011-04-21          9.44
5             2010-01-04        104.55
5             2011-02-03         38.82
...              ...              ...

i’m trying to get a query to return:

select t1.id, max(t1.date), t1.value, t2.id, min(t2.date), t2.value
from tab1 as t1, tab1 as t2
where t1.id = t2.id
and t1.date <= '2011-03-31'
and t2.date >= '2011-04-01'
group by t1.id;

But it is taking forever (db has ~ 1mm lines). I’ve tried various joins but then it seems to ignore the date < and > statements. Basically I want each customers last purchase date and amount before 4/1/2011 and their first purchase and date on or after 4/1/2011. Any suggestions would be great.

Answer 1

Your query is flawed, the columns t1.value and max(t1.date) do not have a relation to one and other.

You need to rewrite it as follows, if you want to know the total purchases per the date selected.

SELECT st1.id, st1.date, st1.total_value, st2.id, st2.date, st2.total_value
FROM (SELECT t1.id, t1.date, sum(t1.value) as total_value
      FROM tab1 t1
      WHERE t1.date <= '2011-03-31'
      GROUP BY t1.id
      HAVING t1.date = MAX(t1.date)
      ) st1
INNER JOIN (SELECT t2.id, t2.date, sum(t2.value) as total_value
           FROM tab1 t2
           WHERE t2.date > '2011-03-31'
           GROUP BY t2.id
           HAVING t2.date = MAX(t2.date)
           ) st2 
  ON (st1.id = st2.id)

Make sure you have an index on id and date

Remarks
id is generally understand as a shorthand for the primary key.
Having a field called id that does not a unique index, is confusing and widely considered a code smell.