Re: [sqlite] "where not exists (union-select)" fails on 2nd where

2005-08-24 Thread Markus Weissmann 

On 24.08.2005, at 03:21, Kurt Welgehausen wrote:


SELECT * FROM PRIM AS P
WHERE NOT EXISTS
(
SELECT REFID FROM REF1 WHERE REF1.REFID=P.ID
UNION
SELECT REFID FROM REF2 WHERE REF2.REFID=P.ID
);



I looks like correct SQL according to the SQLite docs,
but I don't understand why you coded the select that
way. You should get the same result from

   select * from prim as p
   where not exists (select refid from ref1
 where refid=p.id) and
 not exists (select refid from ref2
 where refid=p.id)

I would guess that this form would be more efficient
because if the first test fails, the second sub-select
should not be executed, perhaps saving a complete scan
of ref2.



perfect - thanks a lot!


-Markus

---
Markus W. Weissmann
http://www.mweissmann.de/
http://www.opendarwin.org/~mww/

Re: [sqlite] "where not exists (union-select)" fails on 2nd where

2005-08-23 Thread Kurt Welgehausen 
> SELECT * FROM PRIM AS P
> WHERE NOT EXISTS
> (
> SELECT REFID FROM REF1 WHERE REF1.REFID=P.ID
> UNION
> SELECT REFID FROM REF2 WHERE REF2.REFID=P.ID
> );

I looks like correct SQL according to the SQLite docs,
but I don't understand why you coded the select that
way. You should get the same result from

   select * from prim as p
   where not exists (select refid from ref1
 where refid=p.id) and
 not exists (select refid from ref2
 where refid=p.id)

I would guess that this form would be more efficient
because if the first test fails, the second sub-select
should not be executed, perhaps saving a complete scan
of ref2.

Regards

[sqlite] "where not exists (union-select)" fails on 2nd where

2005-08-23 Thread Markus Weissmann 

Hi folks,

I've got a little problem with a - at least I think so - correct SQL- 
statement:


three tables, two referencing the 1st one

---
SELECT * FROM PRIM AS P
WHERE NOT EXISTS
(
SELECT REFID FROM REF1 WHERE REF1.REFID=P.ID
UNION
SELECT REFID FROM REF2 WHERE REF2.REFID=P.ID
);
---

chokes with "SQL error: no such column: P.ID"; as long as I do not use
a WHERE statement in the 2nd 'inner' SELECT statement, it works as  
expected.


I've worked around this by creating a VIEW from the union of the two
referencing tables so I do not need the UNION in the original query.

Is this a bug or did I just not get the docs?


thanks,

-Markus


PS: sqlite really rocks & the C-API doc is very nice!

---
Markus W. Weissmann
http://www.mweissmann.de/
http://www.opendarwin.org/~mww/