Re: How to force select to return exactly one row

Martin,

Thank you. SELECT statement returns lot of columns.

I tried

select coalesce( (select 1,2 ), null);

but got

ERROR: subquery must return only one column

How to use your suggestion if select returns lot of columns ?

Andrus.

----- Original Message -----
From: Martin
To: Andrus
Cc: pgsql-general(at)postgresql(dot)org
Sent: Monday, June 21, 2010 10:14 PM
Subject: Re: [GENERAL] How to force select to return exactly one row

Try wrapping the entire statement in a COALESCE((statement), <DEFAULT_VALUE>);

-m

2010/6/21 Andrus <kobruleht2(at)hot(dot)ee>

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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Andrus Moor
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