SQL（DB2） - 如果未找到记录则返回零

Question

如何更改此查询以便为找不到行的每个区域显示零？

    proc sql;
create table test as
select count(acct_num) as total_count,
       region
    from
        table1
    group by region
    ;
run;

理想情况下，我希望看到这一点：

Region1   500
Region2   0
Region3   20
Region4   0

Answer 1

假设您有一张包含所需区域的表格，您可以使用left join：

select r.region, count(t.acct_num) as total_count
from regions r left join
     table1 t
     on r.region = t.region
group by r.region;

如果您没有这样的表格，您可以通过以下方式即时创建一个表格：

select r.region, count(t.acct_num) as total_count
from (select 'region1' as region from sysibm.sysdummy1 union all
      select 'region2' from sysibm.sysdummy1 union all
      . . .
     ) r left join
     table1 t
     on r.region = t.region
group by r.region;