Use a case staement to test for a null output, & return whatever you want in the event of it being null, else the actual value:
from the top of my head, something like:
SELECT case when
(select somecolumns
FROM ko
RIGHT JOIN (SELECT 1) _forceonerow ON true
LEFT JOIN t1 ON t1.primarykey= ko.t1foreignkwey
...
LEFT JOIN tn ON tn.primarykey= ko.tnforeignkwey
WHERE ko.primarykey is null or ko.primarykey='someprimarykeyvalue') not null
then (select somecolumns
FROM ko
RIGHT JOIN (SELECT 1) _forceonerow ON true
LEFT JOIN t1 ON t1.primarykey= ko.t1foreignkwey
...
LEFT JOIN tn ON tn.primarykey= ko.tnforeignkwey
WHERE ko.primarykey is null or ko.primarykey='someprimarykeyvalue')
else
0
end
It does require the query to be run twice, so does have extra overhead. You could wrap a function around this to get & store the result & test that, then having stored it you can use it for the output value without a second query. All depends on how much overhead there is in teh query.
HTH,
Brent Wood
Brent Wood
DBA/GIS consultant
NIWA, Wellington
New Zealand
>>> "Andrus" <kobruleht2@hot.ee> 06/22/10 10:12 AM >>>
Autogenerated select statement contains 0 .. n left joins:
SELECT somecolumns
FROM ko
LEFT JOIN t1 ON t1.primarykey= ko.t1foreignkwey
...
LEFT JOIN tn ON tn.primarykey= ko.tnforeignkwey
WHERE ko.primarykey='someprimarykeyvalue';
This select can return only 0 or 1 rows depending if ko row with primary key
'someprimarykeyvalue' exists or not.
Problem:
if there is no searched primary key row in ko database, select should also
return empty row.
To get this result I added right join:
SELECT somecolumns
FROM ko
RIGHT JOIN (SELECT 1) _forceonerow ON true
LEFT JOIN t1 ON t1.primarykey= ko.t1foreignkwey
...
LEFT JOIN tn ON tn.primarykey= ko.tnforeignkwey
WHERE ko.primarykey is null or ko.primarykey='someprimarykeyvalue';
but it still does not return row if primary key row 'someprimarykeyvalue'
does not exist.
How to force this statement to return one row always ?
Andrus.
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