06_non_spatial_queries.Rmd

# Review Non-spatial Queries

Non-spatial queries are queries that don't involve the geometry column (the spatial information) of our table.

We'll start by investigating our *flowlines* data.  The *flowlines* are linear features that carry water from one place to another.  Some are nature features like rivers or streams, others are man-made like canals.

## Let's look at the whole table:

``` SELECT * FROM flowlines; ```

The asterisk (\*) means "everything" or "give me all the columns".  You could read the query as "Select everything from the *flowlines* table."

The result should look very much like the attribute table you explored earlier, but with a couple of additional columns.  The import process added an *id* field and a *geom* field.  The *geom* field contains information that allows the database tool to know where that particular object should be located in space, but unfortunately, it doesn't look like anything we understand as humans.  We'll learn to deal with this column more in a little while.

## Add a WHERE clause: 

``` SELECT * FROM flowlines WHERE ftype = 460; ``` 

This query limits our results to just the rows where the number in the *ftype* column is 460, which corresponds to the natural rivers and streams (not canals).  "Where" in this case does **NOT** indicate location, but rather a condition of the data.

## Add a function: 

``` SELECT COUNT(id) FROM flowlines WHERE ftype = 460; ``` 

Here we've added the function COUNT().  So we've asked the database tool to count all of the IDs but only if they have an FYTYPE of 460.

## Summarize Data

What if we wanted to know how many lines there were of each *ftype*?

``` SELECT ftype, COUNT(id) FROM flowlines GROUP BY ftype; ```

Here, I've asked for a table with the *FTYPE* and the count of each *id*, and finally that it should summarize (group by) the *FTYPE*.

If I don't like the column name that it automatically generates - ```COUNT(id)``` - I can give it an alias with the AS command:

``` SELECT ftype, COUNT(id) AS NumberOfLines FROM flowlines GROUP BY ftype; ```

This is especially handy if you're making a table for people unfamiliar with your data or SQL or if you need the column name to be something specific.