oracle 你能有一个没有 ON 关键字的 INNER JOIN 吗？

Can you have an INNER JOIN without the ON keyword?

提问by Mike Christensen

While debugging into some Oracle code, I came across this query:

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

I'm confused by the line:

我对这条线感到困惑：

INNER JOIN TPM_TASK

I haven't seen a JOINwithout an ONclause before. Also confusing is the line:

我以前没见过JOIN不带ON子句的。同样令人困惑的是这条线：

ON TPM_GROUP.GROUPID = TPM_GROUPTASKS.GROUPID

This seems like a random ONclause without any matching JOIN. The query runs without any errors, and returns a bunch of data, so obvious the syntax is perfectly valid. Can someone shed some light on exactly what's going on here?

这似乎是一个ON没有任何匹配的随机子句JOIN。查询运行没有任何错误，并返回一堆数据，很明显语法是完全有效的。有人可以解释一下这里发生了什么吗？

回答by Justin Cave

Small universe... I ran across a tool generating this syntax yesterday and was rather flummoxed.

小宇宙...昨天我遇到了一个生成这种语法的工具，并且相当困惑。

Apparently,

显然，

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

is equivalent to a nested subquery

相当于嵌套子查询

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

回答by Lamak

I think that this is only a problem of ordering your query (since there are only INNER JOINs, the order of them is not really that important). I rearrenged your query and now it looks like this:

我认为这只是排序查询的问题（因为只有INNER JOINs，所以它们的顺序并不是那么重要）。我重新排列了您的查询，现在看起来像这样：

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 

Does it make more sense to you now?, it does to me.

现在对你来说更有意义吗？对我来说更有意义。

回答by dotjoe

It'd look fine if it had parenthesis in there...

如果里面有括号就好了...

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

but since they are all inner joins I agree with Lamak's answer.

但由于它们都是内部连接，我同意拉马克的回答。