Oracle PIVOT子句中的用户自定义聚合函数

Question

无法在Oracle PIVOT子句中使用用户定义的聚合函数。

我创建了一个用户定义的聚合函数string_agg。我可以在一个简单的陈述中使用它，比如……

select id, string_agg(value) from
(
    select 'user1' as id, 'BMW' as value,   'CAR'      as type from dual    union
    select 'user1' as id, 'Audi' as value,  'CAR'      as type from dual    union
    select 'user2' as id, 'Honda' as value, 'CAR'      as type from dual    union
    select 'user1' as id, 'Dell' as value,  'COMPUTER' as type from dual    union
    select 'user1' as id, 'Sony' as value,  'COMPUTER' as type from dual    union
    select 'user2' as id, 'HP' as value,    'COMPUTER' as type from dual 
)
group by id, type

结果:

ID          TYPE            STRING_AGG(VALUE)
user1       CAR             Audi,BMW
user1       COMPUTER        Dell,Sony
user2       CAR             Honda
user2       COMPUTER        HP

但是，当我尝试在pivot子句中使用相同的函数时

select * from
( 
    select id, type, string_agg(value) as value from
    (
        select 'user1' as id, 'BMW' as value,   'CAR'      as type from dual    union
        select 'user1' as id, 'Audi' as value,  'CAR'      as type from dual    union
        select 'user2' as id, 'Honda' as value, 'CAR'      as type from dual    union
        select 'user1' as id, 'Dell' as value,  'COMPUTER' as type from dual    union
        select 'user1' as id, 'Sony' as value,  'COMPUTER' as type from dual    union
        select 'user2' as id, 'HP' as value,    'COMPUTER' as type from dual 
    )
    group by id, type
)
PIVOT (string_agg(value) FOR id IN ('user1' user1, 'user2' user2) );

我得到以下错误…

ORA-56902: expect aggregate function inside pivot operation

预期结果是…

TYPE        USER1       USER2
COMPUTER    Dell,Sony   HP       
CAR         Audi,BMW    Honda

Answer 1

Pivot不需要在相同的聚合函数上:

select * from
( 
    select id, type, LISTAGG(value) WITHIN GROUP (ORDER BY 1) as value from
    (
        select 'user1' as id, 'BMW' as value,   'CAR'      as type from dual    union
        select 'user1' as id, 'Audi' as value,  'CAR'      as type from dual    union
        select 'user2' as id, 'Honda' as value, 'CAR'      as type from dual    union
        select 'user1' as id, 'Dell' as value,  'COMPUTER' as type from dual    union
        select 'user1' as id, 'Sony' as value,  'COMPUTER' as type from dual    union
        select 'user2' as id, 'HP' as value,    'COMPUTER' as type from dual 
    )
    group by id, type
)
PIVOT (max(value) FOR id IN ('user1' user1, 'user2' user2) );

Answer 2

试试wmsys怎么样?Wm_concat而不是用户定义的聚合?