SQL（DB2）-如果找不到记录，则返回零

Question

如何更改此查询以在没有找到行的每个区域中显示零？

    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，我希望看到以下内容：

Region1   500
Region2   0
Region3   20
Region4   0

Answer 1

假设您有想要的所有区域的表，则可以使用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;

如果没有这样的表，则可以通过以下操作动态创建一个表：

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;