QGIS » QGIS Application

In the layer properties in QGIS Desktop, add the ability to specify the type of Join of two layers. At present only an INNER JOIN is performed.

For example, I wish to implement the following equivalent code within QGIS
i.e. I want to display all records, which have a parent with name "xx"

SELECT * FROM table_1, table_2, table_3
WHERE table_1.foreign_key = table_2.key AND table_3.foreign_key = table_2.key AND
table_2.parent_key = (SELECT table_3.foreign_key, WHERE table_3.name = "xx")

From the following MS SQL Server tables
table_1
with fields - id, foreign_key, geom
table_2
with fields - key, parent_key, etc.
table_3
with fields - id2, foreign_key, name, preferred

Tables 1 and 2 are of the same length
The field "parent_key" allows the objects to be arranged in a hierachical fashion.
Table 3 allows several names to be attached to the same object, with the field "preferred" indicating the preferred name. Hence table_3

is longer than table_2.

At present, if the 3 tables are joined within the Layer properties, then only the first entry from table_3 is included, rather than what is required are all rows, so that the preferred names can be selected.