I'm using QGIS 1.8. Windows 7. I have a table in MS SQL Server 2008 R2 database with two fields: id and density(int). There are several polygons in QGIS. How can I set color of polygion depending on the value of the field density in MS SQL Server (e.g 1-20 polygon is yelllow, 20-40 - green, 40-60 - red)using python console?