mysql - SQL join 3 tables grouped with latest group value -

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i have 3 tables. user, messages , user_analytics following structure:

  • user (userid) - contains users
  • message (messageid(pk),userid(fk),time) - contains messages
  • user_analytics (user_analyticsid(pk),userid(fk),device,time) -
    contains data collected on connection
user : messages (1:n) user : device (1:n)

now know how many messages sent on each day device. therefor first need collect each message device (desktop,ios,android) used send message depending on message time itself. means need user_analytics.time <= message.time , display latest result.

i saw lot solutions greatest-n-per-group didn't work.

i work subquery takes 20 seconds (user_analytics holds 100k records , message 3k... not much):

select  date_format(m.time,'%y-%m-%d') date,         count(*) message_count,         ua.device    message m,         user u left join user_analytics ua on (             u.userid = ua.userid ,             ua.user_analyticsid = ( select max(user_analyticsid)                                     user_analytics                                   userid = m.userid ,                                         time < m.time))   m.userid = u.userid group 1,3;

but looks highly inefficient. other ways achieve same result?

update: forgot mention have important condition on user table. why need join table.

i created sql fiddle give example. implemented jaguar chang's solution 100 times faster mine:

sql fiddle

there's no necessity of joining user table, simplify code this:

select  date_format(m.time,'%y-%m-%d') date,         count(*) message_count,         ua.device    message m,         left join user_analytics ua on (             m.userid = ua.userid ,             ua.user_analyticsid = ( select max(user_analyticsid)                                     user_analytics                                   userid = m.userid ,                                         time < m.time)) group 1,3;

this may not efficient enough, try this:

select  date_format(t2.time,'%y-%m-%d') date,         count(*) message_count,         t2.last_device         (select        @device :=            if(@uid = userid,              if(tbl = 'm' ,@device, device),              if(@uid := userid,device,device)) last_device       ,t1.*                  (select @device := '' , @uid :=0) t0       join           (select 'ua' tbl,userid,time,device user_analytics            union            select 'm' tbl,userid,time,null device messages           ) t1       order userid,time     ) t2 tbl='m' group 1,3;

i guess original purpose divide messages times of connection on device, order messages , connection record time series together, device used last connection every message.

i think approach efficient, since 100k+3k sorting faster 3k*100k*100k join operations

a test sql fiddle demo.


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