problem with inserting a generated seq no into not null field
I have the following generic query which I am trying to use to insert
into a 3 field table
INSERT INTO tb_files (subj, area, file_no) select '4', '8',(SELECT CASE
WHEN (4||8) NOT IN (SELECT (subj||area) FROM tb_files) THEN '1' ELSE
max(file_no)+1 END FROM tb_files GROUP BY (subj||area),subj,area HAVING
subj = '4' AND area = '8');
However the first entry will not go in with a
'null value in column "file_no" violates not-null constraint'
message
Anyone any ideas on this - the CASE statement does not seem to be being
evaluated
On Tue, 08 Jun 2004 12:37:48 +0100, mike <mike@bristolreccc.co.uk>
wrote:
INSERT INTO tb_files (subj, area, file_no) select '4', '8',(SELECT CASE
WHEN (4||8) NOT IN (SELECT (subj||area) FROM tb_files) THEN '1' ELSE
max(file_no)+1 END FROM tb_files GROUP BY (subj||area),subj,area HAVING
subj = '4' AND area = '8');
If there is no row with subj = '4' AND area = '8', then SELECT ...
HAVING returns no rows and therefore max(file_no) is NULL. And NULL+1
is NULL. Try
INSERT INTO tb_files (subj, area, file_no)
SELECT '4', '8', coalesce(max(file_no), 0)+1
FROM tb_files
WHERE subj = '4' AND area = '8';
Servus
Manfred
I have the following generic query which I am trying to use to insert
into a 3 field tableINSERT INTO tb_files (subj, area, file_no) select '4', '8',(SELECT CASE
WHEN (4||8) NOT IN (SELECT (subj||area) FROM tb_files) THEN '1' ELSE
That's not really a good way to detect the existance of a row with those
values. If either subj or area is allowed to be NULL, wierdness occurs
(*). Even if neither is allowed to be null, if the values can ever have
more than one digit wierdness occurs.
(*) - IIRC, even if no row exists with (4,8) as (subj,area), if there's a
row where subj || area is NULL, you will never get true from the NOT IN
clause and the second alternative will always be chosen. NULLs and IN
don't play very well together.