没有ON关键字,你有INNER JOIN吗？

Question

在调试某些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

我对这条线感到困惑:

INNER JOIN TPM_TASK

我以前没见过JOIN没有ON条款的人.线路也令人困惑:

ON TPM_GROUP.GROUPID = TPM_GROUPTASKS.GROUPID

这似乎是一个ON没有任何匹配的随机子句JOIN.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.有人能否详细了解这里究竟发生了什么？

Answer 1

小宇宙......昨天我遇到了一个生成这种语法的工具,而且相当混乱.

显然,

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

等效于嵌套子查询

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 JOINs,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 

你现在对它更有意义吗？它对我有用.