Oracle LEFT OUTER JOIN的问题

Question

In our program, we have a Many-To-Many relation between a table 'Person' and a table 'Phonem'. This is archieved by an join table, 'PersonPhon'.

Person:

PERSID 
NAME
FIRSTNAME
DATEOFBIRTH
TYPE
[...]

PersonPhon:

PEPHPERSID <-- references the person
PEPHPHONID <-- references the phonem

Phonem:

PHONID
PHONEM

Due to a bug, some recent Persons were persisted without a reference to their respective Phonem entries. To read them from the database, I created a statement:

select p.persid from    
Person p left outer join PersonPhon ph 
on p.persid = ph.pephpersid              
where p.type = 'natural'

This statement was meant to give me all Persons with no respective entry in PersonPhon, and, with test data (only Persons without PersonPhon-entries) this works well. However, the statement also selects Persons if they have PersonPhon-entries, so I guess my statement has an error, yet I cannot figure out whats wrong.

Edit:

Entries:

Person-Table

PERSID | NAME | FIRSTNAME | AGE | TYPE (other columns ommitted)
76257713 | Wilko | Roger| 30 | natural
76257714 | Martian | Marvin | 50 | natural

PersonPhon-Table

PEPHPERSID | PEPHPHONID
76257713 | 21000
76257713 | 26000    

Phonem-Table

PHONID | PHONEM
21000 | 4875122
26000 | 7468112
most entries omitted (> 100000)

With the above data, the statement gives:

76257713 
76257713 
76257714 

Which is unexpected behaviour. Expected would be just 76257714 .

If the PersonPhonem-Table is empty, it gives:

76257713 
76257714 

Which looks like the expected behaviour, but seems to be misleading.

Answer 1

If you are trying to find rows in person that don't have an entry in another table, it sounds like you want a not exists rather than a left outer join . You could do a left outer join and then have a where clause that looks to see that the left joined table's values are null but that is generally less readable.

My guess is that you want

SELECT *
  FROM person p
 WHERE NOT EXISTS( SELECT 1
                     FROM PersonPhon ph
                    WHERE p.persid = ph.pephpersid )
   AND <<your additional predicates>>