Question

我花了至少4个小时来解决它，我尝试了很多发布在这里的解决方案，但是我仍然没有解决它。

这是我的查询

SELECT * FROM l_article 
         INNER JOIN accounts_user 
         LEFT JOIN laws_marcacao ON (laws_marcacao.article_id = l_article.id 
                                AND laws_marcacao.user_id = accounts_user.id) 
         WHERE l_article.law_id = 1 and accounts_user.id = 1

在where附近发生错误：

ERROR:  syntax error at or near "where"
LINE 5:                        where l_article.law_id = 1 and accoun...
                               ^

Answer 1

问题是l_article和accounts_user之间的内部联接，它缺少合格的联接。

语法：

T1 { [INNER] | { LEFT | RIGHT | FULL } [OUTER] } JOIN T2 ON boolean_expression
T1 { [INNER] | { LEFT | RIGHT | FULL } [OUTER] } JOIN T2 USING ( join column list )
T1 NATURAL { [INNER] | { LEFT | RIGHT | FULL } [OUTER] } JOIN T2

https://www.postgresql.org/docs/9.2/queries-table-expressions.html

因此，如果要执行笛卡尔乘积，则使用CROSS JOIN而不是INNER JOIN。如果要使用INNER JOIN，则需要具有连接条件，例如USING或ON子句。

查看此sqlfiddle

Answer 2

使联结表脱离最终结果的简单技巧：

SELECT * 
FROM l_article a
JOIN accounts_user u ON EXISTS (
        SELECT * 
        FROM laws_marcacao xx
        WHERE xx.article_id = a.id                        
        AND xx.user_id = u.id
        )
WHERE a.law_id = 1 AND u.id = 1
  ;

使用LEFT JOIN和ON子句时如何解决WHEREerror

2 个答案: