涉及 LISTAGG 的 DB2 SQL

Question

我有一个如下所示的数据集

  DEPT_ID  EMP_NM   STATUS_DATE    LEFT_FLAG      STATUS_CHANGE
    1       ABC      20200131        0            N
    1       DEF      20200204        0            N
    1       DEF      20200504        0            Y
    1       XYZ      20201210        0            N
    1       MNO      20201210        0            N
    1       DEF      20201230        1            N
    1       XYZ      20201230        0            Y
    1       PQR      20210123        0            N
    1       ABC      20210228        1            N
    1       XYZ      20210228        1            N

现在我想生成如下输出

  DEPT_ID  EMP_NM               STATUS_DATE    
    1       ABC                  20200131        
    1       ABC,DEF              20200204  
    1       ABC,DEF              20200504      
    1       ABC,DEF,XYZ,MNO      20201210        
    1       ABC,XYZ,MNO          20201230        
    1       ABC,XYZ,MNO,PQR      20210123        
    1       MNO,PQR              20210228   

我尝试使用 LISTAGG，但无法消除重复项，也无法在 LEFT_FLAG=1 时删除

Answer 1

如果我理解正确，您每次都需要一份员工名单。状态标志似乎必须相关。

这个版本应该可以在 DB2 中工作：

select dept_id, status_date, listagg(emp_nm, ',') within group (order by emp_nm)
from (select t.dept_id, t.status_date, t2.status_date as status_date_2, t2.left_flag, t2.emp_nm,
              row_number() over (partition by t.status_date, t2.dept_id, t2.emp_nm order by t2.status_date desc) as seqnum
      from (select dept_id, status_date
            from t 
            group by dept_id, status_date
           ) t left join
           t t2
           on t2.dept_id = t.dept_id and t2.status_date <= t.status_date
     ) tt2
where seqnum = 1 and left_flag = 0
group by dept_id, status_date;

Here 是一个 dbfiddle。

这个版本不是因为关联子句嵌套得太深，唉，对于 DB2：

select t.dept_id, t.status_date,
       (select listagg(t2.emp_nm, ',') within group (order by t2.emp_nm)
        from (select t2.emp_nm,
                     row_number() over (partition by t2.dept_id, t2.emp_nm order by t2.status_date desc) as seqnum
              from t t2
              where t2.status_date <= t.status_date and
                    t2.dept_id = t.dept_id
             ) t2
        where t2.seqnum = 1 and t2.left_flag = 0
       ) as emps
from t
group by dept_id, status_date;