Question

I have a statement like

TableA

ID    X
1     x1
2     x2
3     x3

TableB

ID    AttributeName      AttributeValue
1     Type               some
2     not                nothing
3     Type               other

I now want a result like

1,x1,some
2,x2,''
3,x3,other

The SQL

SELECT TableA.ID, TableA.X, TableB.AttributeValue
FROM TableA, TableB
WHERE TableA.ID = TableB.ID AND TableB.AttributeName = 'Type'

gives me all IDs with X and TypeDescription where the Attribute Type exists.
But I also want the IDs where no Type is set included – how to reach that?

Answer 1

You need an outer join:

SELECT TableA.ID, TableA.X, TableB.AttributeValue
FROM TableA
LEFT OUTER JOIN TableB ON TableA.ID = TableB.ID AND TableB.AttributeName = 'Type'

This will return a NULL, not an empty string '' for id=2. If you need an empty string instead, use coalesce. On SQL Server it would look like this:

SELECT TableA.ID, TableA.X, COALESCE(TableB.AttributeValue, '')
FROM TableA
LEFT OUTER JOIN TableB ON TableA.ID = TableB.ID AND TableB.AttributeName = 'Type'