"Andrus" <kobruleht2@xxxxxx> wrote:
> 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 ?
It's a bit difficult to decipher what you're looking for
(what do you mean by "empty row"?), but you may want to try
something along the lines of:
| SELECT v.primarykey, ko.somecolumns
| FROM (VALUES ('someprimarykeyvalue')) AS v (primarykey)
| LEFT JOIN ko ON v.primarykey = ko.primarykey
| LEFT JOIN t1 ON t1.primarykey = ko.t1foreignkey
| [...]
| LEFT JOIN tn ON tn.primarykey = ko.tnforeignkey;
Whether that suits your needs depends very much on the data
structure and the tools you use.
Tim
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