MySQL查询GROUP BY两列

Question

I need help with MySQL query
I have this cenary:

table A
- page_id
- rev_id
- date
one page_id can have multiples rev_id

table B
- rev_id
- words
I have what words have in each revision

I need return for each date the quantity of words that I have in the last rev_id in each page_id

Example:

table A
page_id | rev_id   |   date
---------------------------------
 1      |  231     |   2002-01-01
 2      |  345     |   2002-10-12
 1      |  324     |   2002-10-13
 3      |  348     |   2003-01-01

--

table B
rev_id | words
---------------
231    | 'ask'
231    | 'the'
231    | 'if'
345    | 'ask'
324    | 'ask'
324    | 'if'
348    | 'who'

magical sql here edited to show how its calculated {page_id : [words]}

date        |  count(words)
--------------------------
2002-01-01  |    3           { 1:[ask, the, if] }
2002-10-12  |    4           { 1:[ask, the, if], 2:[ask] }
2002-10-13  |    3           { 1:[ask, if], 2:[ask] }
2003-01-01  |    4           { 1:[ask, if], 2:[ask], 3:[who] }

I did this query, but my date are fixed and I need for all dates contained in table revision:

SELECT SUM(q) 
FROM (
    SELECT COUNT(equation) q 
    FROM revision r, equation e
    WHERE r.rev_id in (
        SELECT max(rev_id) 
        FROM revision 
        WHERE date < '2006-01-01' 
        GROUP BY page_id
    ) 
    AND r.rev_id = e.rev_id
    GROUP BY date
) q;

---

Solved

My friend help-me to create query to solve my problem!

select s.date, count(words) from
(select d.date, r.page_id, max(r.rev_id) as rev_id 
    from revision r, (select distinct(date) from revision) d 
    where d.date >= r.date group by d.date, r.page_id) s
join words e on e.rev_id = s.rev_id
group by s.date;

Answer 1

I think this is a basic join and group by :

select a.date, count(*)
from a join
     b
     on a.rev_id = b.rev_id
group by a.date;

EDIT:

Oh, I think I get it. This is a cumulative thing. That makes it more complicated.

select d.date,
       (select count(*)
        from a join
             b
             on a.rev_id = b.rev_id
        where a.date <= d.date and
              a.rev_id = (select max(a2.rev_id) from a a2 where a2.date = a.date and a2.date <= d.date)
       ) as cnt
from (select date from a) d;

But that won't work in MySQL because of the nesting of the correlation clause. So, we can restructure the logic as:

select a.date, count(*)
from (select a.*,
             (select max(a2.rev_id)
              from a a2
              where a2.date <= a.date and a2.page_id = a.page_id
             ) as last_rev_id
      from a
     ) a join
     b
     on a.last_rev_id = b.rev_id
group by a.date;