PostgreSQL情况下多列给出错误列不存在

Question

是否可以在postgresql中使用两个不同的列运行case语句？

我想使用CASE语句将整数映射到特定值。 我可以使用ds.ordinal做到这一点，但是当我添加dcs.status时，出现以下错误： column "follow_up" does not exist 。

是否可以在一个SELECT语句的不同列上使用多个case语句？

case when dcs.status = 0 then "follow_up" end as "follow_up"而不返回错误case when dcs.status = 0 then "follow_up" end as "follow_up"如何获得case when dcs.status = 0 then "follow_up" end as "follow_up" ？

SELECT DISTINCT ON (pd.id)
           case when ds.ordinal = 1 then s.name end as "primary_specialty",
           case when ds.ordinal = 2 then s.name end as "secondary_specialty",
           case when dcs.status = 0 then "follow_up" end as "follow_up"

    FROM potential_doctors AS pd
         INNER JOIN patient_profile_potential_doctors as pppd on pd.id = pppd.potential_doctor_id
         INNER JOIN doctor_taxonomies AS dt on pd.id = dt.potential_doctor_id
         INNER JOIN taxonomies AS t on dt.taxonomy_id = t.id
         INNER JOIN doctor_profiles AS dp on pd.npi = dp.npi
         INNER JOIN doctor_specialties AS ds on dp.id = ds.doctor_profile_id
         INNER JOIN specialties AS s on ds.specialty_id = s.id
         INNER JOIN doctor_creation_notes as dcs on dcs.doctor_profile_id = dp.id

    WHERE dp.approved IS FALSE

Answer 1

我希望查询看起来像这样；

SELECT DISTINCT ON (pd.id)
       (case when ds.ordinal = 1 then s.name end) as primary_specialty,
       (case when ds.ordinal = 2 then s.name end) as secondary_specialty,
       (case when dcs.status = 0 then 'follow_up' end) as follow_up
FROM . . . 
WHERE dp.approved IS FALSE
ORDER BY pd.id;

换句话说，我认为您只需要在字符串常量周围加上单引号即可。

我做了另外两个更改。 如果您使用的是DISTINCT ON ，那么您应该有一个ORDER BY ，括号中的表达式用于DISTINCT ON作为ORDER BY的第一个键。 您可以添加更多键以获取最早，最新，最大，最小或任何您想要的行。

另外，我从列名中删除了双引号。 您显然对SQL中的引号感到困惑。 我的建议是仅对字符串和日期常量使用单引号。 不要使用双引号，而应通过仅使用有效字符为标识符命名来避免使用双引号。