Task 5: Selecting Features with a Query

If you don't know where to look on a map to find the features you are looking for, or if you are looking for features with particular attributes (fields), use Query to locate features more specifically, using SQL Structured Query Language A standard computer language for accessing and manipulating databases. queries Criteria for selecting features or layers on a map using the SQL language.. You can search for features from several fields in one layer.

A query is a way to search data from a database table The database location for data from a single layer. Each column in the table represents specific data (called "fields") for that layer. The rows (called "records") represent individual features (instances) of items in the layer. For example, the Parcel layer contains many parcels (rows) which have a number of fields, like street, address, APN, owner, etc. Usually there is a separate layer for these as well, so you can display them separately., which contains the data behind a layer. The resulting data is exactly the same information that you find using the Identify button, but in the form of a single table rather than pages.

When you have found the items you are searching for, you can zoom in to the specific features on the map, where you can treat them as selected features or view statistics of the selected features.

If there are external tables connected with a layer, you can also query them.

At the very end are some examples to practice with.

Try it out!

Create query

1. Activate the Layer with the features you are interested in on the Layers Tab.

2. Click the Query tab on the Right Pane.

3. Select the Layer Name from the drop-down box, which shows all activated layers.

4. Select a Field Each column in a database table represents specific data (called "fields") for the particular layer. (See "Table")  (feature) Name from the next drop-down list, which shows all the fields available in the database for that layer.

5. Select an operator (equals, greater, lesser etc.). To search for a partial detail, use the "like" operator (for example, "like"+"C" to find all the Materials that start with "C".)

6. The Samples drop-down box shows all of the different values of the selected field. Either select one there, or type in a value in the Search for box.

7. Click Run Query.

8. The results are shown in the Results pane.

7. Look at the SQL Query string "StormdrainLines where ([ST_DATE]='12/10/1971') to see how it is written.

8. See how many features the query returns at the beginning of the SQL Structured Query Language A standard computer language for accessing and manipulating databases. (See "Query" and "Table".) Query string.

9. Click the Zoom link to select an item on the map.

Narrow the search using several fields with the AND button

If you want to narrow the results of the query to fewer features use the AND button to search using several fields to include all the features that have both the first criteria and the second. In this example, we first searched for all the Stormdrain Lines earlier than a particular date. Narrow it down to only those made with the "CMP" Material.

1. Click AND.

2. Select another field, operator and search data. (Here we selected the Material and Equal To CMP)

3. Click Run Query.

4. Look at the new Query String.

5. Check to see how many features the revised query found.

Note: Use OR if you want to expand the results to include everything that has either the first criteria or the second criteria.

Zoom to All Records

• Click the Zoom to All Records button to select all the records. Then you can export the data to a spreadsheet using the Reporting and Mailing Labels tool on the Main Toolbar.

Save a query

• To save a query to use again, enter the name in the box and click Save.

• To run it again, click the name in the lowest box and click Run.

View Statistics about a particular feature

1. Make sure that your pop-up blocker enables http://www.geovieweronline.net/.

2. Click the Statistics button to view a pop-up A small webpage without a top menu bar often used for advertising, but used here for certain functions. A pop-up blocker blocks the ads, but blocks these functions if the site isn't specifically allowed. with a list of fields for the selected features.

3. Click a field name to view the Minimum and Maximum Values for that field and the Sum of all the values for the selected features.

Note: Statistics are only meaningful with features with a numeric value, and the sum only where a sum makes sense, as in total area.

Query on External Data

If there are tables associated with a layer, use this query to view the tables.

If you'd like to practice with some queries, here are a few to try:

Different maps have different feature names, so you may have to use your imagination to solve these. Or search for features that you need in your work.

1. Find all mains (Layer Name) with diameters (Field Name) that are less than or equal to (Operator) 12 (Search for).

2. Find all mains with diameters less than or equal to 12 AND Pipeclass CL150 (like 150).

3. Find all parcels owned by someone named Johnson.

4. Find all parcels owned by someone named Johnson AND with an area greater than 10000.

5. Find all meters with an install date prior to 1950.

6. Find all meters with an install date prior to 1950 AND a diameter greater than 4.