一。查询A表的所有字段,还要查询和A表关联的B表的C字段的个数,条件是A.Fnum=B.Cnum
在上例中,学习人数和完成人数之前的字段都是A表的字段,学习人数和完成人数需要关联查询B表。
select FCOURSEWARE_NAME,fid ,fcourseware_type ,ftime_long ,flanguages ,fowner ,fcontributor ,fon_line_time,stu.sc,s.c,fstate from COURSEWARE c left join (select count(1) as sc,course_number from user_course_study_info where course_number is not null group by course_number ) stu on stu.course_number = c.fcourse_id left join (select count(1) as c,course_number from user_course_study_info where BROWSE_SCORE=100 and course_number is not null group by course_number) s on s.course_number = c.fcourse_id
二。 查A的记录时,同时要查询出和A关联的C表总记录数,C表不直接和A表关联,C表和B表是多对一,B和A是多对一。同时也要查出D表和A对应的记录数,D表和A表关联。
select * from (select t.fid, t.fcourse_code, t.fcourse_name, t.funit, t.flevel, t.FCREATETIME, sum(arr.tc) as tc, sum(choose.tc2) as tc2 from course_info t left join (select count(1) as tc, fid, fcourse_id from teach_arrangement group by fid, fcourse_id) arr on arr.fcourse_id = t.fid left join (select count(1) as tc2, FTEACH_ARRANGEMENT_ID from TEACHPLAN_STUDENT_CHOOSE group by FTEACH_ARRANGEMENT_ID) choose on choose.FTEACH_ARRANGEMENT_ID = arr.fid group by t.fid, t.fcourse_code, t.fcourse_name, t.funit, t.flevel, t.FCREATETIME) temp left join (select count(1) as tc3, fcourse_id from courseware group by fcourse_id) ware on ware.fcourse_id = temp.fid
查询结果如下: