Howto build a SQL statement with using IDs that might not be available in the table?

Question

Using Microsoft SQL Server 2008, let\'s say there is a table1 that keeps the selected ids of provinces, districts, communes and villages. And then there is table2 with the

Answer 1

An OUTER JOIN won't work here, because you don't want to have all elements from table2, but only those where a corresponding element exists in table 1.

You would want to do something like this:

SELECT tbl1.province, tbl1.district, tbl1.commune, tbl1.village 
FROM dbo.table2 AS tbl2 
INNER JOIN dbo.table1 AS tbl1
ON tbl1.province = tbl2.province_id 
AND tbl1.district = tbl2.district_id 
AND (tbl1.commune is NULL OR (tbl1.commune = tbl2.commune_id)) 
AND (tbl1.village is NULL OR (tbl1.village = tbl2.village_id))