SQL SELECT字段依赖于行中的另一个字段

Question

我正在尝试从字段AS“initial_cost”中选择一个值，但是该值位于不同的列中，具体取决于channel_id字段的值，如果channel_id为1，则它在field_id_4中，如果它是2则则为; s在field_id_10。

我尝试了下面的各种突变，但无济于事，

SELECT (CASE WHEN channel_id = 1 
        THEN field_id_4 
        FROM exp_channel_data 

        WHEN channel_id = 2 
        THEN field_id_10 FROM exp_channel_data 
        END) as initial_cost

有人可以帮忙吗？

Answer 1

喜欢这个吗？

select title
      ,entry_date
      ,case when channel_id = 1 then field_id_4
            when channel_id = 2 then field_id_10
        end as initial_cost
  from exp_channel_data;

Answer 2

或使用case <column> when <value>代替case when <condition>：

select  case channel_id 
        when 1 then field_id_4
        when 2 then field_id_10
        end as initial_cost
from    exp_channel_data

Answer 3

SELECT CASE WHEN channel_id = 1 THEN field_id_4 
   WHEN channel_id = 2 THEN field_id_10 END as intialcost
   FROM exp_channel_data