Oracle sql 计算单列中不同值的实例

Question

我有一个带有状态列的表。我想要一个 Oracle sql 查询，它将仅在一行中列出每个状态中的行数。
例如，如果我的 table 是

Table A
Id       Status  Fkey
1         20      500
2         20      500  
3         30      501
4         40      501
5         30      502

输出应该是

Fkey     Count_status20     Count_status30    Count_status40
500        2                      0                 0
501        0                      1                 1

这里稍微有点扭曲

Table B 
FKey TKey 
500   1001 
501   1001
502   1002 

现在输出应该是

TKey Count_status20     Count_status30    Count_status40 
1001     2                     1                    1 
1002     0                     1                    0

Answer 1

如果您使用的是 Oracle 11g，那么您可以使用 PIVOT功能:

select *
from
(
  select tkey, status, 
    status as col
  from tableB b
  left join tableA a
    on a.fkey = b.fkey
) src
pivot
(
  count(status)
  for col in ('20' as Count_Status20, 
              '30' as Count_Status30,
              '40' as Count_Status40)
) piv;

见 SQL Fiddle with Demo

如果您没有使用 Oracle11g，那么您可以使用带有 CASE 的聚合函数陈述:

select tkey, 
  count(case when status = 20 then 1 else null end) as Count_Status20,
  count(case when status = 30 then 1 else null end) as Count_Status30,
  count(case when status = 40 then 1 else null end) as Count_Status40
from tableB b
left join tableA a
  on b.fkey = a.fkey
group by tkey

见 SQL Fiddle with Demo