oracle – 当列值中没有sys_connect_by_path定界符时,为什么会得

我在Oracle版本上测试了这个：
11.2.0.3.0
12.1.0.2.0

以下查询激发ORA-30004错误,但我的脱离符为’ – > ‘未在任何列值中行使：

with temptable as (
  select '2624' as id,'ninechars' as label,'' as parentid from dual union 
  select '2625' as id,'erewrettt' as label,'2624' as parentid from dual union 
  select '2626' as id,'Im stumped' as label,'' as parentid from dual union 
  select '2627' as id,'- Unknown -' as label,'' as parentid from dual
)
select sys_connect_by_path(label,' -> ' ) 
from temptable
start with parentid is null 
connect by prior id = parentid;

一些调查：

• Changing the value “ninechars” to “ninecharsx” allows the query to work
• Changing the value “ninechars” to “abcdefghi” also breaks the query
  • It seems like all nine character values here break the query
• Leaving the value as “ninechars” and removing the last union statement,which is not connected to any of the other records,allows
  the query to work
• Changing the delimiter from ‘ -> ‘ to ‘ *> ‘ allows the query to work

题
ORA-30004错误的来历是什么？为什么Oracle以为脱离符是作为列值的一部门呈现的？

编辑：感激bobdylan在评述中留下的这个pastebin.com/Ad1edFcJ 链接有助于声名题目

办理要领

SQL> with t (id,label,parentid,reportlevel,fake_connect_by_path) as (
  2  select id,0 as reportlevel,' -> ' || label as fake_connect_by_path
  3    from temptable
  4   where parentid is null
  5   union all
  6  select tt.id,tt.label,tt.parentid,reportlevel + 1,t.fake_connect_by_path || ' -> ' || tt.label as fake_connect_by_path
  7    from temptable tt
  8    join t on t.id = tt.parentid
  9  )
 10  select fake_connect_by_path
 11    from t;
FAKE_CONNECT_BY_PATH
--------------------------------------------------------------------------------
 -> ninechars
 -> Im stumped
 -> - Unknown -
 -> ninechars -> erewrettt

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