计算同一表行中表列的更改

Question

我正在努力弄清楚如何做这样的事情。我有一个看起来像这样的 SQL 表。我想添加一列，该列总计每个产品在一年中拥有的服务商 ID 的数量。在名为“服务年数”的表中：

+-------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+----------------------+
| Product ID  | Jan Servicer ID | Feb Servicer ID | Mar Servicer ID | Apr Servicer ID | May Servicer ID | Jun Servicer ID | Jul Servicer ID | Aug Servicer ID | Sep Servicer ID | Oct Servicer ID | Nov Servicer ID | Dec Servicer ID | Years Servicer Count |
+-------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+----------------------+
| ID-001-2015 | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-02      | SRVR-ID-02      | 2                    |
+-------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+----------------------+
| ID-002-2015 | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | 1                    |
+-------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+----------------------+
| ID-002-2016 | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-01      | SRVR-ID-02      | SRVR-ID-02      | SRVR-ID-02      | SRVR-ID-02      | SRVR-ID-02      | SRVR-ID-02      | SRVR-ID-03      | SRVR-ID-03      | 3                    |
+-------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+----------------------+

我正试图集中精力计算一列中不同值的数量。朝着正确方向的任何推动都会令人惊叹。

Answer 1

一个选项在子查询中使用union all 将列取消透视到行，然后count(distinct)：

select
    t.*,
    (
        select count(distinct servicer_id)
        from (
            select t.jan_servicer_id as servicer_id
            union all select t.feb_servicer_id
            union all select t.mar_servicer_id
            ...
            union all select t.dec_servicer_id
        ) t
    ) as years_servicer_count
from mytable t

如果对于 netezza 来说嵌套太多，那么另一种方法是连接：

select t.*, s.years_servicer_count
    
from mytable t
inner join (
    select product_id, count(distinct servicer_id) as years_servicer_count
    from (
        select product_id, jan_servicer_id as servicer_id from mytable
        union all select product_id, feb_servicer_id from mytable
        union all select product_id, mar_servicer_id from mytable
        ...
        union all select product_id, dec_servicer_id from mytable
    ) t
    group by product_id
) s on s.product_id = t.product_id