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I need some help converting MySQL to Oracl join syntax

Posted on 2006-07-17
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Last Modified: 2012-05-05
Hi, I know MySQL and never used Oracle before, the join syntax I use in MySQL isn't working for me here.  Can anyone spot the issue?

the problem is sometimes a session has no particiapants, so a "WHERE p.session_id = spl.session_id" doesn't work, which is why I'm using a join...only it's still not returning any data on sessions that have no participants, of which there are many.  Every other constraint is working fine.  

here's the full table def (table names in caps) and query:

 # CONFERENCES  
 # conference_id
 # name
 # description
 # displayorder
 
 # PUBSESSIONS  
 # session_id
 # abbreviation
 # title
 # abstract
 # session_type
 # session_properties
 # length_name
 # minutes
 # isconfevent
 
 
 # PUBSESSIONSTRANS  
 # session_id
 # abbreviation
 # title
 # abstract
 # session_type
 # techlevel
 # length_name
 # minutes
 # isconfevent
 
 
 # SESCONFLINKS  
 # session_id
 # conference_id
 
 
 # SESPARTICIPANTLINKS  
 # person_id
 # session_id
 # role
 
 
 # SESPARTICIPANTS  
 # person_id
 # firstname
 # lastname
 # jobtitle
 # companyname
 # bio
 
 
 # SESPARTICIPANTSTRANS  
 # person_id
 # firstname
 # lastname
 # jobtitle
 # companyname
 # bio
 
 
 # SESSCHEDULE  
 # session_id
 # month
 # day
 # year
 # time
 # room
 
 
 # SESSCHEDULETRANS  
 # session_id
 # month
 # day
 # year
 # time
 # room
 
 
 # SESTRACKLINKS  
 # session_id
 # track_id
 
 
 # TRACKS  
 # track_id
 # name
 # description
 # displayorder
 
 
 # TRACKSTRANS
 # track_id
 # name
 # description
 # displayorder
 SELECT *,
 ss.month,
 ss.day,
 ss.year,
 TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'),'HH24:MI') as time,  
 room,
 spl.person_id,
 spl.role,
 sp.firstname,
 sp.lastname,
 sp.jobtitle,
 sp.companyname,
 sp.sp.bio  
 FROM PUBSESSIONS p
 LEFT JOIN SESSCHEDULE ss on p.session_ID = ss.session_ID
 LEFT JOIN SESSPARTICIPANTLINKS spl ON p.session_id = spl.session_id
 LEFT JOIN SESSPARTICIPANTS sp ON sp.person_id = spl.person_id  
 WHERE (p.session_type NOT LIKE 'Tutorials' AND p.session_type NOT LIKE 'Conference Within A Conference')  
 AND spl.role NOT LIKE 'Conference Chairman'  
 ORDER BY ss.day, TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'), 'HH24:MI'),  p.session_type desc, p.session_id, spl.role desc
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Question by:bakum
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12 Comments
 
LVL 25

Expert Comment

by:jrb1
ID: 17123437
I'll create the tables and test, but I wonder if you have to have "left outer join" in the Oracle syntax:

 SELECT *,
 ss.month,
 ss.day,
 ss.year,
 TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'),'HH24:MI') as time,  
 room,
 spl.person_id,
 spl.role,
 sp.firstname,
 sp.lastname,
 sp.jobtitle,
 sp.companyname,
 sp.sp.bio  
 FROM PUBSESSIONS p
 LEFT OUTER JOIN SESSCHEDULE ss on p.session_ID = ss.session_ID
 LEFT OUTER JOIN SESSPARTICIPANTLINKS spl ON p.session_id = spl.session_id
 LEFT OUTER JOIN SESSPARTICIPANTS sp ON sp.person_id = spl.person_id  
 WHERE (p.session_type NOT LIKE 'Tutorials' AND p.session_type NOT LIKE 'Conference Within A Conference')  
 AND spl.role NOT LIKE 'Conference Chairman'  
 ORDER BY ss.day, TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'), 'HH24:MI'),  p.session_type desc, p.session_id, spl.role desc
0
 
LVL 25

Expert Comment

by:jrb1
ID: 17123492
OK, that's not it.  How about this:

SELECT *,
 ss.month,
 ss.day,
 ss.year,
 TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'),'HH24:MI') as time,  
 room,
 spl.person_id,
 spl.role,
 sp.firstname,
 sp.lastname,
 sp.jobtitle,
 sp.companyname,
 sp.sp.bio  
 FROM PUBSESSIONS p
 LEFT OUTER JOIN SESSCHEDULE ss on p.session_ID = ss.session_ID
 LEFT OUTER JOIN SESSPARTICIPANTLINKS spl ON p.session_id = spl.session_id
 LEFT OUTER JOIN SESSPARTICIPANTS sp ON sp.person_id = spl.person_id  
 WHERE (p.session_type NOT LIKE 'Tutorials' AND p.session_type NOT LIKE 'Conference Within A Conference')  
 AND (spl.role NOT LIKE 'Conference Chairman'  or spl.role is NULL)
 ORDER BY ss.day, TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'), 'HH24:MI'),  p.session_type desc, p.session_id, spl.role desc
 
0
 
LVL 14

Expert Comment

by:sathyagiri
ID: 17123588
See if this works
 SELECT p.*,
 ss.month,
 ss.day,
 ss.year,
 TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'),'HH24:MI') as time,  
 room,
 spl.person_id,
 spl.role,
 sp.firstname,
 sp.lastname,
 sp.jobtitle,
 sp.companyname,
 sp.sp.bio  
 FROM PUBSESSIONS p,SESSCHEDULE ss, SESSPARTICIPANTLINKS spl,SESSPARTICIPANTS sp
 WHERE p.session_id = ss.session_id(+) and  p.session_id = spl.session_id(+) and sp.person_id = spl.person_id(+) and
(p.session_type NOT LIKE 'Tutorials' AND p.session_type NOT LIKE 'Conference Within A Conference')  
 AND spl.role NOT LIKE 'Conference Chairman'  
 ORDER BY ss.day, TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'), 'HH24:MI'),  p.session_type desc, p.session_id, spl.role desc
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LVL 25

Expert Comment

by:jrb1
ID: 17123648
Yes that was it.  When I have a row in your 4 tables in the query, I pull back data.  When I delete the LINK, the query stops pulling the data.  And when I change the criteria to include the NULL check, it works.  Another way to specify this is:

 SELECT *,
 ss.month,
 ss.day,
 ss.year,
 TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'),'HH24:MI') as time,
 room,
 spl.person_id,
 spl.role,
 sp.firstname,
 sp.lastname,
 sp.jobtitle,
 sp.companyname,
 sp.sp.bio
 FROM PUBSESSIONS p
 LEFT JOIN SESSCHEDULE ss on p.session_ID = ss.session_ID
 LEFT JOIN SESSPARTICIPANTLINKS spl ON p.session_id = spl.session_id and spl.role NOT LIKE 'Conference Chairman'
 LEFT JOIN SESSPARTICIPANTS sp ON sp.person_id = spl.person_id
 WHERE (p.session_type NOT LIKE 'Tutorials' AND p.session_type NOT LIKE 'Conference Within A Conference')
 ORDER BY ss.day, TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'), 'HH24:MI'),  p.session_type desc, p.session_id, spl.role desc
0
 

Author Comment

by:bakum
ID: 17131702
jrb1 - both of those statements give me the following error:
Invalid sql statement:
ORA-00923: FROM keyword not found where expected

Sathyagiri - your statement gives me this error:
Invalid sql statement:
ORA-01417: a table may be outer joined to at most one other table

Thanks for your help.  ANy further suggestions?
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LVL 25

Accepted Solution

by:
jrb1 earned 500 total points
ID: 17131907
Yes.  lose the "*," at the top.  I didn't touch that part of the query you posted.  But it won't really work.

 SELECT  ss.month,
 ss.day,
 ss.year,
 TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'),'HH24:MI') as time,
 room,
 spl.person_id,
 spl.role,
 sp.firstname,
 sp.lastname,
 sp.jobtitle,
 sp.companyname,
 sp.sp.bio
 FROM PUBSESSIONS p
 LEFT JOIN SESSCHEDULE ss on p.session_ID = ss.session_ID
 LEFT JOIN SESSPARTICIPANTLINKS spl ON p.session_id = spl.session_id and spl.role NOT LIKE 'Conference Chairman'
 LEFT JOIN SESSPARTICIPANTS sp ON sp.person_id = spl.person_id
 WHERE (p.session_type NOT LIKE 'Tutorials' AND p.session_type NOT LIKE 'Conference Within A Conference')
 ORDER BY ss.day, TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'), 'HH24:MI'),  p.session_type desc, p.session_id, spl.role desc

or

SELECT  ss.month,
 ss.day,
 ss.year,
 TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'),'HH24:MI') as time,  
 room,
 spl.person_id,
 spl.role,
 sp.firstname,
 sp.lastname,
 sp.jobtitle,
 sp.companyname,
 sp.sp.bio  
 FROM PUBSESSIONS p
 LEFT OUTER JOIN SESSCHEDULE ss on p.session_ID = ss.session_ID
 LEFT OUTER JOIN SESSPARTICIPANTLINKS spl ON p.session_id = spl.session_id
 LEFT OUTER JOIN SESSPARTICIPANTS sp ON sp.person_id = spl.person_id  
 WHERE (p.session_type NOT LIKE 'Tutorials' AND p.session_type NOT LIKE 'Conference Within A Conference')  
 AND (spl.role NOT LIKE 'Conference Chairman'  or spl.role is NULL)
 ORDER BY ss.day, TO_CHAR(TO_TIMESTAMP(ss.time, 'HH24:MI'), 'HH24:MI'),  p.session_type desc, p.session_id, spl.role desc


0
 

Author Comment

by:bakum
ID: 17132737
Excellent!  Two questions:
1)Can you explain the diff between a left join and a left outer join?
2)this seems to be the magic constraint: LEFT JOIN SESSPARTICIPANTLINKS spl ON p.session_id = spl.session_id and spl.role NOT LIKE 'Conference Chairman'
   why does adding spl.role NOT LIKE 'x' to this constraint return data where there is no spl.session_id?  That I do not understand.
0
 
LVL 25

Expert Comment

by:jrb1
ID: 17132909
1) There is no difference.  It is just a matter of syntax.  In some databases, only one or the other is valid.  I always use "left outer join" in oracle, but they obviously support both wordings.

2) Go back to your original query.  You left join the table SESSPARTICIPATNLINKS, so even if there is no row in this table, the row is returned.  Then in your where statement, you say where "spl.role NOT LIKE 'Conference Chairman'".  Unfortunately, NULL values work different than you might imagine.  If spl.role is NULL (there was no row in this table) and it is compared with 'Conference Chairman', the comparison always fails:

select * from dual where null = 'Conference Chairman';
select * From dual where null <> 'Conference Chairman';

Neither or these return a row.  That WHERE statement filtered your results.  My first solution solved it like this:

select * from dual where null <> 'Conference Chairman' or null is null;

That returns a row.  You could also have said:

select * from dual where nvl(null,' ') <> 'Conference Chairman';

The other way to get rid of this problem is to move the criteria to the OUTER JOIN "ON" statement.  There, the filtering occurs on the SESSPARTICIPANTLINKS table before trying to join in to the other tables.
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LVL 25

Expert Comment

by:jrb1
ID: 17132914
And thanks for the points.  You pushed me to the "Wizard" level.  Much appreciated.
0
 

Author Comment

by:bakum
ID: 17133560
This is great.  You truly are a wizard.  If I may, then, the crucial difference in my first question is not the difference between a left join and an inner join but instead an inner and an outer join.  If I am not mistaken, an inner join returns a row even if there is no row in the table.  An outer join, will not reutrn the row if the the row is null.  Right?
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LVL 25

Expert Comment

by:jrb1
ID: 17133912
No, an inner join only returns matching rows:

tableA
key  data
1   a
2   b
3   c

tableB
key  moredata
1     x
3     y

select * from tableA
inner join tableB
on tableA.key = tableB.key

a.key a.data b.key b.moredata
1      a        1        x
3      c        3        y

select * From tableA
left outer join tableB
on tableA.key = tableB.key

a.key a.data b.key b.moredata
1      a        1        x
2      b
3      c        3        y

There is also a RIGHT OUTER JOIN, so you are correct, the crucial difference is between an outer join and an inner join.  You were correctly using an OUTER JOIN.  However, the sticking point is, when you specify the criteria in a WHERE statement, you are doing a where on the results of the JOIN.  So, in my OUTER JOIN example above, if you said:

select * From tableA
left outer join tableB
on tableA.key = tableB.key
where tableB.key <> 6

This would return:

a.key a.data b.key b.moredata
1      a        1        x
3      c        3        y

The issue is with the NULLs on tableB for that middle row and how the comparisons work.  Even though (in my view) NULL is different than 6, that is not how SQL treats it.  It treats it as neither equal to and not equal to.  If you are doing a "WHERE" on a column that is the OUTER JOINed table, you have to be very careful.  You will most likely need to add a NULL check of some kind, so you don't filter out rows accidentally.
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Author Comment

by:bakum
ID: 17135099
wow.  thanks!  I never could have gotten that from reading a website I think.
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