如下一个sql拼接片段
case_parent_platform =" case when from_platform in (2, 3, 7) then '1' " \
"when from_platform in (21, 23, 24, 25, 26, 27, 28) then '2' " \
"when from_platform in (12, 20) then '3' " \
"when from_platform in (0) then '4' " \
"else '5' end as parent_platform, "
见过，不是太熟悉，很少使用，这里总结一下case when 的使用方法
1、满足条件的列，对值进行替换
如原表table
假如我想将verify_code这一列满足条件的值进行替换，如
select case when verify_code='808096' then 'new' else 'old' end as vt from table
查询结果如下
2、替代where条件，如
select
ck_out_profit, ck_a_profit
from (
SELECT supplier_name,
round(sum(case when sale_type in (1,2) then out_profit else null end),4) as ck_out_profit,
round(sum(case when sale_type in (1,2,3) then gross_profit else null end),4) as ck_a_profit
from bi_mdata.dm_order_send_detail
where date_str>='2020-11-22' and date_str<='2020-11-22' and supplier_name !=''
group by supplier_name） a
如上，不同的字段使用的条件不同，我们可以使用case when，来解决，否则就需要使用联接语法了。
