Question

在调试某些Oracle代码时，我遇到了这个问题：

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

我对这条线感到困惑：

INNER JOIN TPM_TASK

我之前没有看到JOIN没有ON条款。线路也令人困惑：

ON TPM_GROUP.GROUPID = TPM_GROUPTASKS.GROUPID

这似乎是一个没有任何匹配ON的随机JOIN子句。查询运行时没有任何错误，并返回一堆数据，因此显而易见的是语法完全有效。有人能否确切了解这里到底发生了什么？

Answer 1

小宇宙......昨天我遇到了一个生成这种语法的工具，而且很笨拙。

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

我认为这只是排序查询的问题（因为只有INNER JOIN s，它们的顺序并不那么重要）。我重新调整了你的查询，现在它看起来像这样：

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

现在对你有意义了吗？它对我有用。

Answer 3

如果它有括号那么看起来很好......

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

但由于他们都是内心联盟，我同意拉马克的回答。

没有ON关键字，你有INNER JOIN吗？

3 个答案: