任务表字段task :主键id, 任务详情taskdetail, 外键oid, 外键eid, 外键did1, 外键did2
订单表字段orders : 主键id, 订单名称name
员工表字段emp : 主键id, 员工姓名empname
部门表字段dept : 主键id, 部门名称name
其中任务表, 四个外键(oid,eid,did1,did2)关联三张表(orders,emp,dept)
需求: 查询任务详情, 订单名称, 员工姓名, 任务实施部门名称, 协助部门名称
查询语句怎么写?
http://blog.csdn.net/github_37767025/article/details/67636061
select taskdetail,name,empname,name from task t,orders o,emp e,dept d where t.oid = o.id and t.eid = e.id and t.did1 = d.id and t.id = 主表ID
left join关联起来咯
select taskdetail,name,empname,name from task t,orders o,emp e,dept d where t.oid = o.id and t.eid = e.id and t.did1 = d.id and t.id = 主表ID
select r.taskdetail , m.name, t.empname, q.name from task r left join orders m
where r.id = m.id
left join emp t
where t.id = r.id
left join dept q
where q.id = r.id
select t.taskdetail,o.name,e.empname,d.name from task t
inner join orders o on t.oid = o.id
inner join emp e on t.eid = e.id
inner join dept d on t.did1 = d.id