Question

此查询在MySQL中正常工作，但在PostgreSQL中没有：

select
concat(hc.id, hl.languagecode) AS id,
hc.id AS category_id,
hl.languagecode AS languagecode
from language hl
join category hc
left join categorytranslation hct ON hl.languagecode = hct.languagecode and hc.id = hct.category_id;

在PostgreSQL中我偶尔会遇到错误：

错误：输入结束时的语法错误LINE 9：.... languagecode = hct.languagecode和hc.id = hct.category_id ^查询失败PostgreSQL说：输入结束时的语法错误

或者是空的结果。我正在使用Postico进行测试。

它出了什么问题？

我想要做的是得到这样的结果：

 select
        concat(hc.id, hl.languagecode) AS id,
        hc.id AS category_id,
        hl.languagecode AS languagecode,
        hc.slug AS slug
from category hc, language hl

但我也想加入一个翻译'categorytranslation'的表格。如果有可用的翻译而不是“类别”表。为此我修改了这样的查询：

    SELECT
            concat(hp.id, hl.languagecode) AS id,
            hp.id AS id,
            hl.languagecode AS languagecode,
            hpt.languagecode as translang,
            CASE WHEN (hpt.languagecode is not null and hpt.slug is not null and trim(hpt.slug) <> '')
              THEN hpt.slug
              ELSE hp.slug
            END AS slug,
    from language hl
join category hc
left join categorytranslation hct ON hl.languagecode = hct.languagecode and hc.id = hct.category_id;

Answer 1

在PostgreSQL中，每个连接都需要一个连接条件短语。在您的查询中，表之间的关系似乎是hl -> hct -> hc;然后查询变为：

SELECT hc.id || languagecode AS id,
       hc.id AS category_id,
       languagecode
FROM language hl
LEFT JOIN hapis_hatracocategorytranslation hct USING (languagecode)
JOIN category hc ON hc.id = hct.category_id;

请注意，通过在第一个连接条件中使用USING短语，两个表中的languagecode列之间不存在歧义，因此您可以省略选择列表中的别名。

查询在MySQL中运行良好，但在PostgreSQL中运行不正常

1 个答案: