nested inner join with select query in mysql

Question

hello folks can anyone tell me what is this best way i mean any other way which will have less line of code as compare to this let me show query first

 select agent.*, count(que.id)  queue_count    
 from table agent 
 left join (select * from table2 q 
            INNER JOIN table3 p on q.path_id=p.id 
            where q.status=1 p.name='demo') que 
   on que.agent_id=agent.id 
 left join table3 path on path.id=que.path_id    
 group by agent.id 
 order by queue_count

i have 3 table now i want to join all table and inner select again im join 2 table ie table 2 and 3 with where clause

Answer 1

To get all information on an agent, then left-joining to get counts from another table, you would typically need to do the group by all non-aggregate fields... If your agent table has a bunch of fields, you would be better to pre-aggregate your sub-query to just get counts on a per-agentId basis... Then you have AT MOST one record per agent and can just simple LEFT-JOIN on that agent.

I assume your table references of "table", "table2", "table3" are actually fake name of actual tables, but using the ALIASES of "agent", "p", and "q" respectively within the query.

select 
      agent.*, 
      que.AgentQueueCount queue_count
   from 
      table agent
         left join 
         (select
                q.agent_id,
                count(*) AgentQueueCount
             from 
                table2 q 
                   INNER JOIN table3 p 
                      on q.path_id = p.id 
                      AND p.name='demo'
             where 
                q.status = 1 
             group by
                q.agent_id ) que 
           on agent.id = que.agent_id 
    order by 
       que.AgentQueueCount

Here, the sub-query is already inner-joined on the matching path ID and path name.

Answer 2

Remove table keyword and add AND in the condition.

 select agent.id, count(que.id)  queue_count    
 from agent 
 left join (select * from table2 q 
            INNER JOIN table3 p on q.path_id=p.id 
            where q.status=1 AND p.name='demo') que 
   on que.agent_id=agent.id 
 left join table3 path on path.id=que.path_id    
 group by agent.id 
 order by queue_count