On Tue, Aug 21, 2012 at 8:07 PM, <h...@tbbs.net> wrote: >>>>> 2012/08/21 16:35 -0600, Larry Martell >>>> > I am trying to write a query that selects from both a correlated > subquery and a table in the main query, and I'm having a lot of > trouble getting the proper row count. I'm sure this is very simple, > and I'm just missing it. I'll try and present a simple example. For > this example, there are 27 rows, organized like this: > > > mysql> select count(*), target_name_id, ep, wafer_id from data_cst > where target_name_id = 44 group by target_name_id, ep, wafer_id; > +----------+----------------+------+----------+ > | count(*) | target_name_id | ep | wafer_id | > +----------+----------------+------+----------+ > | 6 | 44 | 1,1 | 16 | > | 3 | 44 | 1,1 | 17 | > | 6 | 44 | 1,2 | 16 | > | 3 | 44 | 1,2 | 17 | > | 6 | 44 | 1,3 | 16 | > | 3 | 44 | 1,3 | 17 | > +----------+----------------+------+----------+ > 6 rows in set (0.00 sec) > > I need to get an average of a column grouped by target_name_id, ep as > well as the average of the averages grouped by target_name_id, ep, > wafer_id, and I also need the count of the rows in the target_name_id, > ep group. My query is getting the correct averages, but incorrect row > counts: > > mysql> select count(*), target_name_id, ep, avg(bottom), avg(averages) > from (select avg(bottom) as averages, target_name_id as t, ep as e > from data_cst where target_name_id = 44 group by target_name_id, ep, > wafer_id) x, data_cst where target_name_id = t and ep = e group by > target_name_id, ep; > +----------+----------------+------+-------------+-----------------+ > | count(*) | target_name_id | ep | avg(bottom) | avg(averages) | > +----------+----------------+------+-------------+-----------------+ > | 18 | 44 | 1,1 | 21.8056667 | 21.85458330000 | > | 18 | 44 | 1,2 | 121.7984444 | 121.83983335000 | > | 18 | 44 | 1,3 | 349.7634444 | 349.75016665000 | > +----------+----------------+------+-------------+-----------------+ > 3 rows in set (0.01 sec) > > The count for each row should be 9. What do I need in my count() to be > counting the right thing? > <<<<<<<< > Your trouble lys in the joining; in effect, you are joining a row with > wafer_id 16 with a row with wafer_id 17, and also a row with wafer_id 17 with > a row with wafer_id 16. > > A further advantage to using the now standard form of joining, as Rick James > bids you do, is that one can add further conditions to it: > > select count(*), target_name_id, ep, avg(bottom), avg(averages) > from (select avg(bottom) as averages, target_name_id, ep > from data_cst > where target_name_id = 44 > group by target_name_id, ep, wafer_id) x > JOIN data_cst > ON target_name_id = x.target_name_id and ep = x.ep and wafer_id < x.wafer_id > group by target_name_id, ep > > The inequality, maybe, will give you what you want.
Not, wafer_id < x.wafer_id, but wafer_id = x.wafer_id - adding that makes it work the way I want. Thanks!! -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql
