无法通过此内部联接获取数据（MYSQL / PHP）

Question

我有3张桌子，我试图从列中返回一个列，这让我哭了，为什么它不起作用：

$projectId = 54971033
$id = 53189015

        SELECT     
            iR.author,
            i.dateCreated,
            i.lastModified,
            i.value,
            u.username
        FROM
            informationRelationships iR
        INNER JOIN
            information i ON
            iR.linkId = i.id
        INNER JOIN
            users u ON
            iR.author = u.id    
        WHERE
            iR.contactRef = '$id' AND
            iR.projectRef = '$projectId' AND
            iR.type = 'Project'                    

为什么它没有返回什么想法？

Answer 1

author为零，请尝试使用LEFT JOIN：

SELECT     
    iR.author,
    i.dateCreated,
    i.lastModified,
    i.value,
    u.username
FROM
    informationRelationships iR
LEFT JOIN
    information i ON
    iR.linkId = i.id
LEFT JOIN
    users u ON
    iR.author = u.id    
WHERE
    iR.contactRef = '$id' AND
    iR.projectRef = '$projectId' AND
    iR.type = 'Project'