Question

我正在尝试计算所有未平仓头寸，“paposition”表保存所有可用头寸，“员工”表保存所有处于该头寸的员工。当我运行以下声明时，我收到了

Department     Job Code     Count(*)

10             2            1

10             1            1

但我期待这个;因为“职务代码”中目前没有员工“3”

Department     Job Code     Count(*)

10             3            0

10             2            1

10             1            1

如何将工作代码3的计数显示为“0”或“null”也可以接受

select pos.department, pos.job_code, count(*)
from paposition pos
left join employee emp
on (pos.department = emp.department
and pos.job_code = emp.job_code)
where pos.job_code in ('1', '2', '3')
and pos.end_date = '01-Jan-1700'
and (emp.emp_status like 'A%'
or emp.emp_status like 'L%')
and emp.department = '0010'
group by pos.department, pos.job_code
order by pos.department, pos.job_code

Answer 1

问题是您要通过在left outer join子句中添加emp列来撤消where。

您需要将条件移至on子句：

select pos.department, pos.job_code, count(*)
from paposition pos left join
     employee emp
     on (pos.department = emp.department and
        pos.job_code = emp.job_code and
        (emp.emp_status like 'A%' or emp.emp_status like 'L%') and emp.department = '0010'
where pos.job_code in ('1', '2', '3') and
      pos.end_date = '01-Jan-1700' and
group by pos.department, pos.job_code
order by pos.department, pos.job_code;

（或者，您也可以在NULL和where的{{1}}子句中检查emp.emp_status是否为有效值。）

SQL Left Join不返回“0”或null

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