使用case语句时，PostgreSQL列必须出现在GROUP BY子句中或在聚合函数中使用

Question

我正在使用case语句计算两列， primary_specialty和secondary_specialty 。 这很好，但是，我想在pd.id上执行GROUP BY并收到以下错误：

column "pppd.created_at" must appear in the GROUP BY clause or be used in an aggregate function 。

所需的输出是每个pd一行，并具有primary_specialty和secondary_specialty的列

SELECT pd.id,
       pd.npi,
       pppd.created_at AS "date_submitted", 
       pppd.converted_at AS "date_approved", 
       dp.created_at AS "date_profile_created",
       t.description AS "npi_specialty",
       case when ds.ordinal = 1 then s.name end as "primary_specialty",
       case when ds.ordinal = 2 then s.name end as "secondary_specialty"

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

Answer 1

这可能是您想要的查询：

SELECT pd.id, pd.npi, pppd.created_at AS "date_submitted", pppd.converted_at AS "date_approved", 
       dp.created_at AS "date_profile_created",
       t.description AS "npi_specialty",
       max(case when ds.ordinal = 1 then s.name end) as "primary_specialty",
       max(case when ds.ordinal = 2 then s.name end) as "secondary_specialty"
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
GROUP BY pd.id, pd.npi, pppd.created_at,  pppd.converted_at, t.description

Answer 2

使用DISTINCT ON （pd.id）代替GROUP BY

SELECT DISTINCT ON (pd.id) pd.id,
           pd.npi,
           pppd.created_at AS "date_submitted", 
           pppd.converted_at AS "date_approved", 
           dp.created_at AS "date_profile_created",
           t.description AS "npi_specialty",
           case when ds.ordinal = 1 then s.name end as "primary_specialty",
           case when ds.ordinal = 2 then s.name end as "secondary_specialty"

    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

Answer 3

如果按一个或多个列分组，则只能选择这些列或聚合函数。

因为要对许多行进行分组，所以每个pd.id可能有许多“ primary_specialty”。 但是，如果您从数据库模式中假设集合中只有一个不同的值，则可以使用聚合函数（如MAX）来获取所需的值。 像这样：

SELECT pd.id,
       MAX(case when ds.ordinal = 1 then s.name end) as "primary_specialty",
       MAX(case when ds.ordinal = 2 then s.name end) as "secondary_specialty"