Spatial Databases - Desktop GIS: Mapping the Planet with Open Source Tools - page 104

Figure 7.5: PostGIS query builder in QGIS
First we open the Add PostGIS Table(s) dialog box, connect to our
database, and scroll through the list of layers until we find the gnis
layer. Instead of clicking it and adding it to the map, we double-click
to open the PostgreSQL Query Builder. You'll notice a strong similarity
between this and the query builder we used in Section 3.5 , Advanced
Search, on page 62 . In fact, they share common roots and function in
essentially the same fashion. There is a slight difference in the opera-
tors available, but otherwise once you know how to use one, you can
easily navigate the other. The difference of course is that now we are
querying a real database instead of a shapefile. In Figure 7.5 , you can
see the query builder populated with the parameters for our first layer
(schools) and the results of clicking the Test button.
The query we executed to create schools returned 90 rows. Once we click
OK in the query builder, we are returned to the Add PostGIS Table(s)
dialog box.