PostgreSQL SELECT 结果具有不同的 id，更喜欢另一个 table 的特定值

Question

我有一个 some_dictionary table 和一个 some_dictionary_language table 具有多种语言的数据（以及对 some_dictionary 的引用）。

我需要在 some_dictionary.id 上获取唯一值，首选给定语言的结果，如果不是默认值。

给定 sql:

create table some_dictionary(
    id bigserial primary key,
    some_text varchar(5),
    some_array integer[]
);

create table some_dictionary_language(
    id bigserial primary key,
    some_dictionary_id bigint not null REFERENCES some_dictionary(id),
    language varchar(64) not null,
    name varchar(128) not null
);

insert into some_dictionary (some_text, some_array)
values
    ('text2', '{1, 32, 2}'),
    ('text1', '{5, 9, 1}'),
    ('text4', '{1, 97, 4}'),
    ('text3', '{616, 1, 55}'),
    ('text5', '{8, 1}'),
    ('text6', '{1}');

insert into some_dictionary_language (some_dictionary_id, language, name)
values
    (2, 'POLISH', 'nazwa2'),
    (1, 'ENGLISH', 'name1'),
    (3, 'ENGLISH', 'name3'),
    (2, 'ENGLISH', 'name2'),
    (1, 'POLISH', 'nazwa1'),
    (1, 'SPANISH', 'nombre1'),
    (4, 'SPANISH', 'nombre1'),
    (5, 'ENGLISH', '5name'),
    (6, 'ENGLISH', '6name'),
    (6, 'POLISH', 'nazwa5'),
    (5, 'POLISH', 'nazwa6');

给定条件参数：

langugage = 'POLISH' or if not, default = 'ENGLISH'
phrase in some_text or name = 'na'
element in some_array = 1
page = 1 size = 10

我的 select 语句没有区别：

select d.id, d.some_text, d.some_array, dl.name, dl.language  
from some_dictionary d 
join some_dictionary_language dl on d.id = dl.some_dictionary_id
where dl."language" in ('POLISH', 'ENGLISH')
and (d.some_text ilike '%na%' or dl.name ilike '%na%')
and 1 = ANY(d.some_array)

select 结果：

d.id    d.some_text d.some_array    dl.name     dl.lanugage
2   text1       {5,9,1}     nazwa2          POLISH
1   text2       {1,32,2}    name1       ENGLISH
3   text4       {1,97,4}    name3       ENGLISH
2   text1       {5,9,1}     name2       ENGLISH
1   text2       {1,32,2}    nazwa1          POLISH
5   text5       {8,1}       5name       ENGLISH
6   text6       {1}     6name       ENGLISH
6   text6       {1}     nazwa5          POLISH
5   text5       {8,1}       nazwa6          POLISH

预期 select 结果在 d.id 和首选语言 POLISH 上不同，否则默认为 ENGLISH：

d.id    d.some_text d.some_array    dl.name     dl.lanugage
1   text2       {1,32,2}    nazwa1          POLISH
2   text1       {5,9,1}     name2       POLISH
3   text4       {1,97,4}    name3       ENGLISH (default!)
5   text5       {8,1}       nazwa6          POLISH
6   text6       {1}     6name       POLISH

我试过这样做：

select distinct on (id) * from (
    select d.id, d.some_text, d.some_array, dl.name, dl.language  
    from some_dictionary d 
    join some_dictionary_language dl on d.id = dl.some_dictionary_id
    where dl."language" in ('POLISH', 'ENGLISH')
    and (d.some_text ilike '%na%' or dl.name ilike '%na%')
    and 1 = ANY(d.some_array)
    order by case when dl."language" = 'POLISH' then 1 end
) sub offset 0 row fetch next 10 rows only;

但它没有正常工作：

d.id    d.some_text d.some_array    dl.name     dl.lanugage
1   text2       {1,32,2}    nazwa1          POLISH
2   text1       {5,9,1}     name2       ENGLISH
3   text4       {1,97,4}    name3       ENGLISH
5   text5       {8,1}       nazwa6          POLISH
6   text6       {1}     6name       ENGLISH

Answer 1

确定 DISTINCT ON 如何选择其记录的 ORDER BY 应与 DISTINCT ON 本身处于同一级别，而不是在子查询中。

如果您这样做，错误消息会告诉您问题所在，您必须先按 DISTINCT ON 列排序，然后再按 tie-breaker 列排序。像这样：

select distinct on (id) d.id, d.some_text, d.some_array, dl.name, dl.language  
from some_dictionary d 
join some_dictionary_language dl on d.id = dl.some_dictionary_id
where dl."language" in ('POLISH', 'ENGLISH')
and (d.some_text ilike '%na%' or dl.name ilike '%na%')
and 1 = ANY(d.some_array)
order by id, case when dl."language" = 'POLISH' then 1 end;

当 DISTINCT ON 查询没有 ORDER BY 时，它只是组成一个仅由 DISTINCT ON 列组成的查询，而每个组中保留的行可以任意选择。

PostgreSQL SELECT 结果具有不同的 id，更喜欢另一个 table 的特定值

PostgreSQL SELECT result with a distinct ids that prefers specific values from another table

postgresql

select

unique

distinct

distinct-on