mysql - mysql中如何使用连接？

Question

有两个表 tbldoctor 和 tblschedule

tbl医生

 doc_id(PK)    docMrId        docfname
      1          22             manish
      2          23             rahul
      3          22             ashish
      4          24             ahemad
      5          22             narendra
      6          22             akshat

表计划

  doctor_id(FK)    mr_id       schedule_date
     1              22          2012-06-12
     1              22          2012-06-13
     3              22          2012-06-14
     3              22          2012-06-14
     4              24          2012-06-12
     4              24          2012-06-12
     5              22          2012-06-14
     5              22          2012-06-15
     5              22          2012-06-12

我想要的是所有医生ID的列表以及tblschedule表中重复的特定医生的计数，其中schedule_date参数和mr_id在这里提供，我们假设mr_id = 22和schedule_date在2012-06-01到2012-06-31之间

输出应该看起来像

  doc_id         docfname      count
    1               manish       2
    3               rahul        2
    5               narendra     3
    6               akshat       0

Answer 1

select d.doc_id, docfname, count(mr_id) as count
from tbldoctor d
left outer join tblschedule s on s.doctor_id = d.doc_id
where mr_id = 22 
and schedule_date between '2012-06-01' and '2012-06-31'
group by s.doctor_id

编辑

select d.doc_id, 
       docfname, 
       sum(case when mr_id = 22 
                then 1 
                else 0 
           end) as count
from tbldoctor d
left outer join tblschedule s on s.doctor_id = d.doc_id
and schedule_date between '2012-06-01' and '2012-06-31'
group by s.doctor_id

SQLFiddle example

编辑2

怎么样

select d.doc_id, docfname, count(mr_id) as count
from tbldoctor d
left outer join tblschedule s on s.doctor_id = d.doc_id and mr_id = docmrid
where docmrid = 22 
and (schedule_date between '2012-06-01' and '2012-06-31' or mr_id is null)
group by s.doctor_id
order by d.doc_id

SQLFiddle example