我有一个名为员工时间表的表:
empsheet_id|employee_id|timesheet_status|last_update
该表允许经理访问所有员工时间表。一个员工可以有多个时间表。我只想显示每个员工的最新条目。我在手册中读到我必须编写一个按组最大子查询并与inner join
left join
,但我不确定如何在这里进行。
到目前为止,这是我的查询:
$sqlempsheets="SELECT * FROM employeetimesheets JOIN employees ON employeetimesheets.employee_id=employees.employee_id WHERE employeetimesheets.timesheet_status='Pending Approval'";
$resultempsheets=mysqli_query($db,$sqlempsheets);
试试这个:
select *
from employeetimesheets t
join (
select employee_id,
max(empsheet_id) as empsheet_id
from employeetimesheets
group by employee_id
) t2 on t.employee_id = t2.employee_id
and t.empsheet_id = t2.empsheet_id
join employees e on t.employee_id = e.employee_id
where t.timesheet_status = 'Pending Approval';
或使用left join
:
select t.*, e.*
from employeetimesheets t
left join employeetimesheets t2 on t.employee_id = t2.employee_id
and t.empsheet_id < t2.empsheet_id
join employees e on t.employee_id = e.employee_id
where t.timesheet_status = 'Pending Approval'
and t2.employee_id is null;