您可以在没有ON关键字的情况下进行内连接吗？

Question

在调试一些Oracle代码时，我遇到了这个查询：

SELECT TPM_TASK.TASKID FROM TPM_GROUP 
INNER JOIN TPM_USERGROUPS ON TPM_GROUP.GROUPID = TPM_USERGROUPS.GROUPID 
INNER JOIN TPM_TASK
INNER JOIN TPM_GROUPTASKS ON TPM_TASK.TASKID = TPM_GROUPTASKS.TASKID 
INNER JOIN TPM_PROJECTVERSION ON TPM_TASK.PROJECTID = TPM_PROJECTVERSION.PROJECTID AND TPM_TASK.VERSIONID = TPM_PROJECTVERSION.VERSIONID 
INNER JOIN TPM_TASKSTAGE ON TPM_TASK.STAGEID = TPM_TASKSTAGE.STAGEID 
INNER JOIN TPM_PROJECTSTAGE ON TPM_PROJECTVERSION.STAGEID = TPM_PROJECTSTAGE.STAGEID 
ON TPM_GROUP.GROUPID = TPM_GROUPTASKS.GROUPID

我被这句话搞糊涂了：

INNER JOIN TPM_TASK

我以前从未见过没有ON子句的JOIN。同样令人困惑的是这句话：

ON TPM_GROUP.GROUPID = TPM_GROUPTASKS.GROUPID

这看起来像是一个没有任何匹配JOIN的随机ON子句。查询运行时没有任何错误，并且返回了一堆数据，很明显，语法是完全有效的。有人能解释一下这里到底发生了什么吗？

Answer 1

小宇宙..。昨天我遇到了一个生成这种语法的工具，这让我非常困惑。

显然，

FROM a 
     INNER JOIN b
     INNER JOIN c ON (b.id = c.id)
     ON (a.id = c.id)

等同于嵌套子查询

FROM a
     INNER JOIN (SELECT <<list of columns>>
                   FROM b
                        INNER JOIN c ON (b.id=c.id)) c
             ON (a.id = c.id)

Answer 2

我认为这只是一个查询排序的问题(因为只有INNER JOIN，它们的顺序并不是很重要)。我重新提出了你的查询，现在看起来是这样的：

SELECT TPM_TASK.TASKID 
FROM TPM_GROUP 
INNER JOIN TPM_USERGROUPS 
    ON TPM_GROUP.GROUPID = TPM_USERGROUPS.GROUPID 
INNER JOIN TPM_GROUPTASKS 
    ON TPM_GROUP.GROUPID = TPM_GROUPTASKS.GROUPID
INNER JOIN TPM_TASK
    ON TPM_TASK.TASKID = TPM_GROUPTASKS.TASKID 
INNER JOIN TPM_PROJECTVERSION 
    ON TPM_TASK.PROJECTID = TPM_PROJECTVERSION.PROJECTID 
    AND TPM_TASK.VERSIONID = TPM_PROJECTVERSION.VERSIONID 
INNER JOIN TPM_TASKSTAGE 
    ON TPM_TASK.STAGEID = TPM_TASKSTAGE.STAGEID 
INNER JOIN TPM_PROJECTSTAGE 
    ON TPM_PROJECTVERSION.STAGEID = TPM_PROJECTSTAGE.STAGEID 

对你来说更有意义吗?对我来说更有意义。

Answer 3

如果里面有括号的话看起来还不错...

SELECT TPM_TASK.TASKID 
FROM 
    TPM_GROUP 
    INNER JOIN TPM_USERGROUPS ON TPM_GROUP.GROUPID = TPM_USERGROUPS.GROUPID 
    INNER JOIN (
        TPM_TASK
        INNER JOIN TPM_GROUPTASKS ON TPM_TASK.TASKID = TPM_GROUPTASKS.TASKID 
        INNER JOIN TPM_PROJECTVERSION ON TPM_TASK.PROJECTID = TPM_PROJECTVERSION.PROJECTID 
            AND TPM_TASK.VERSIONID = TPM_PROJECTVERSION.VERSIONID 
        INNER JOIN TPM_TASKSTAGE ON TPM_TASK.STAGEID = TPM_TASKSTAGE.STAGEID 
        INNER JOIN TPM_PROJECTSTAGE ON TPM_PROJECTVERSION.STAGEID = TPM_PROJECTSTAGE.STAGEID 
    ) ON TPM_GROUP.GROUPID = TPM_GROUPTASKS.GROUPID

但是因为它们都是内部连接，所以我同意Lamak的回答。