问题描述
我有以下查询返回所需的数据,但是对于联接表,我想限制返回的行数,并且最好能够为每个联接表指定。 我尝试将limit与select本身结合使用,但似乎不受支持。
这可能吗?我正在使用Postgres 11。
select array_to_json(array_agg(t)) from (
select
tbl_327.field_43,tbl_327.field_1,tbl_327.field_2,jsonb_agg(distinct jsonb_build_object('id',tbl_332.id,'data',tbl_332.fullname)) as field_7,tbl_312.id,tbl_312.fullname)) as field_33
from schema_1.tbl_327 tbl_327
left join schema_1.tbl_327_to_tbl_332_field_7 field_7 on field_7.tbl_327_id=tbl_327.id
left join schema_1.tbl_332_customid tbl_332 on tbl_332.id = field_7.tbl_332_id
left join schema_1.tbl_327_to_tbl_312_field_33 field_33 on field_33.tbl_327_id=tbl_327.id
left join schema_1.tbl_312_customid tbl_312 on tbl_312.id = field_33.tbl_312_id
group by tbl_327.field_43,tbl_327.field_2
) t
已更新 这是我的新查询。我简化了它,但是问题是它不再返回正确的数据。对于field_4字段,它正在重播与记录无关的行/数据。我有什么问题吗?
select array_to_json(array_agg(t)) from (
select
tbl_342.field_1,tbl_342.field_2,tbl_342.id,tbl_312.fullname)) as field_4
from schema_1.tbl_342 tbl_342
left join lateral (
select distinct field_4.*
from schema_1.tbl_342_to_tbl_312_field_4 field_4
where field_4.tbl_342_id=tbl_342.id
limit 50) field_4 on true
left join lateral (
select distinct tbl_312.*
from schema_1.tbl_312_customid tbl_312
where tbl_312_id = field_4.tbl_312_id
limit 5
) tbl_312 on true
group by tbl_342.field_1,tbl_342.id
) t
解决方法
一种方法是将每个left join
变成横向联接;然后可以在每个子查询中设置限制:
select array_to_json(array_agg(t)) from (
select
tbl_327.field_43,tbl_327.field_1,tbl_327.field_2,jsonb_agg(distinct jsonb_build_object('id',tbl_332.id,'data',tbl_332.fullname)) as field_7,tbl_312.id,tbl_312.fullname)) as field_33
from schema_1.tbl_327 tbl_327
left join lateral (
select field_7.*
from schema_1.tbl_327_to_tbl_332_field_7 field_7
where field_7.tbl_327_id=tbl_327.id
order by ...
limit 5
) field_7 on true
left join lateral (
select tbl_332.*
from schema_1.tbl_332_customid tbl_332
where tbl_332.id = field_7.tbl_332_id
order by ??
limit 5
) tbl_332 on true
left join lateral ...
group by tbl_327.field_43,tbl_327.field_2
) t
请注意,您需要使用order by
和limit
才能获得稳定的结果-您可以将查询中的问号替换为新的列或一组列。