Question

我有两张桌子：

语言，作为我语言的索引。

isolanguage
"de"
"en"
"es"
"fi"
"fr"
"no"
"pl"
"ru"

翻译，我存储地方的翻译：

Name, translation, isolanguage
"Umeå Airport";"Flughafen Umeå";"de"
"Umeå Airport";"Umeå Airport";"en"
"Umeå Airport";"Aeropuerto de Umeå";"es"
"Umeå Airport";"Uumajan lentoasema";"fi"

我想要获得的是语言表中每种语言的翻译表中所有元素的列表。

预期结果：

"Umeå Airport";"Flughafen Umeå";"de"
"Umeå Airport";"Umeå Airport";"en"
"Umeå Airport";"Aeropuerto de Umeå";"es"
"Umeå Airport";"Uumajan lentoasema";"fi"
"Umeå Airport";NULL;"fr"
"Umeå Airport";NULL;"no"
"Umeå Airport";NULL;"pl"
"Umeå Airport";NULL;"ru"

关键是我需要所有语言，是否有翻译。

我正在尝试左连接查询，但无效，它只显示两个表中的元素（不包括NULLS）

select * from languages a
left  join translations b
on (a.isolanguage = b.isolanguage)

"Umeå Airport";"Flughafen Umeå";"de"
"Umeå Airport";"Umeå Airport";"en"
"Umeå Airport";"Aeropuerto de Umeå";"es"
"Umeå Airport";"Uumajan lentoasema";"fi"
NULL;NULL;"fr"
NULL;NULL;"no"
NULL;NULL;"pl"
NULL;NULL;"ru"

Answer 1

你可以使用

SELECT Name, translation, isolanguage
FROM 
translations
WHERE
language.isolanguage=translation.isolanguage AND
language.isolanguage = 'de' OR
language.isolanguage = 'fr' OR .......

Answer 2

您可以使用：

select name, isolanguage, translation
from (
    select distinct t.name, l.isolanguage
    from translations t
    cross join languages l
    ) t
left join translations
using (name, isolanguage)
order by 1, 2;

     name     | isolanguage |    translation     
--------------+-------------+--------------------
 Umea Airport | de          | Flughafen Umea
 Umea Airport | en          | Umea Airport
 Umea Airport | es          | Aeropuerto de Umea
 Umea Airport | fi          | Uumajan lentoasema
 Umea Airport | fr          | 
 Umea Airport | no          | 
 Umea Airport | pl          | 
 Umea Airport | ru          | 
(8 rows)

具有所有可能组合的左连接查询

2 个答案: