SQL（DB2）-如果找不到記錄，則返回零

Question

如何更改此查詢以在沒有找到行的每個區域中顯示零？

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

理想情況下，我希望看到以下內容：

Region1   500
Region2   0
Region3   20
Region4   0

Answer 1

假設您有想要的所有區域的表，則可以使用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;

如果沒有這樣的表，則可以通過以下操作動態創建一個表：

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;