Question

我想加入七张桌子：

Table   programs
Column  id    program_name    program_description
        1     Self Help       Self Help Description...
        2     Wellness        Wellness Description...
        3     Education       Education Description...
______________________________________________________

Table   county
Column  id    county_name
        1     Stark
        2     Portage
        3     Wayne
_________________________

Table   services
Column  id    service_name    service_description
        1     Counseling      Counseling Description...
        2     Group Therapy   Group Therapy Description...
        3     Evaluation      Evaluation Description...
__________________________________________________________

Table   population
Column  id    population_name
        1     Adults
        2     Children
        3     Youth
_____________________________

Table   program_county
Column  id    program_id    county_id
        1     1             2
        2     1             3
        3     2             1
        4     2             2
_____________________________________

Table   program_service
Column  id    program_id    service_id
        1     1             2
        2     1             3
        3     2             1
        4     2             2
        5     2             3
______________________________________

Table   program_population
Column  id    program_id    population_id
        1     1             3
        2     2             1
        3     2             3
        4     3             1
_________________________________________

我正在尝试编写一个查询，该查询将为每个程序返回一行并检索program_county，program_services和program_population表中的相关行，并查找这些服务的名称，填充和县每个都在一个字段中显示它们。像：

id   program_name    program_description         Counties           Services                                 Population Served
1    Self Help       Self Help Description...    Portage, Wayne     Group Therapy, Evaluation                Youth
2    Wellness        Wellness Description        Stark, Portage     Counseling, Group Therapy, Evaluation    Adults, Youth

我知道我必须使用连接和GROUP_CONCAT，但我确实很丢失。

Answer 1

如果您想要查看所有程序，无论它们是与县，服务还是人口相关联，您都希望使用外部联接。同样，您应该在连接的值周围使用coalesce()来正确处理NULL值。

这样的事情应该有效：

select programs.id, programs.program_name, programs.program_description,
  group_concat(distinct coalesce(county.county_name,'')) as "Counties",
  group_concat(distinct coalesce(services.service_name,'')) as "Services",
  group_concat(distinct coalesce(population.population_name,'')) as "Population Served"
from programs 
  left outer join program_county on program_county.program_id = programs.id
  left outer join county on county.id = program_county.county_id
  left outer join program_service on program_service.program_id = programs.id
  left outer join services on services.id = program_service.service_id
  left outer join program_population on program_population.program_id = programs.id
  left outer join population on population.id = program_population.population_id
group by programs.id, programs.program_name, programs.program_description
order by programs.id

MySQL GROUP_CONCAT和多个查找表

1 个答案: