Pitney Bowes
MapInfo Pro™ Monthly Journal
ninja Be the Query Ninja

Selecting all of the objects of a certain type


The Query Ninja is back with a technique to select all of the objects of a certain type, (points, lines, regions, etc). This can be helpful in a number of ways. One common use is to ensure consistency within a large table. For example, let's say you have a field in a table that denotes the area of each region. If you find a value of zero in this column, it could either mean the area was not included for that row or that particular object is a point or line, instead of being a region.

Selecting all of the objects of a certain type

To select all of the objects of a certain type, you use the Str$() function and apply it to the map object. It is very easy to do.

Below is a screen shot with the SQL Select dialog box. The example here is we are checking to see if any objects in the World table are points.

SQL

Explanation - what is Str$(Obj)?

Str$() is a function that will take an input and change it into a set of characters. For example a number can be treated as text, perhaps to append values instead of adding them.

Obj is a reference to the Object column of the table.

So in short, Str$(obj) returns a text descriptor of the object type.

Object types:

Any of the following object types may be used in the query:

"Point", "Multipoint", "Line", "Polyline", "Region", "Collection", "Rectangle", "Rounded Rectangle", "Arc", "Ellipse", or "Text".

For example: Str$(obj) = "Point" will select all of the point objects in a table.

Select all of the objects that are not of a specific type:

Let's say you have a table that you are expecting to be all regions and you want to see if any objects are not a region. You can use the not equal to operator.

Str$(obj) <> "Region"

What if there is no object?

Note: Str$(obj) will return a null string ( "" ) if there is no object associated with a row. To select all rows in a table that have no associated map object (for example, all ungeocoded rows after a geocoding operation).

You can use this condition: Str$(obj)="" to select all rows without an object. However, there is a different method that will usually be faster.

Select * from your table where not obj

This article from the August 2012 issue explains this in more detail.

Need the basics on using the SQL capabilities in MapInfo Professional?

This article from the July 2012 issue provides a basic introduction:

Questions, comments, criticisms, suggestions?

We welcome all input on this article. Or on the journal. Or if you have questions. A good place to start a discussion is in the LinkedIn Group we have set up as a companion to this journal. Click here to visit this group.

Article by Tom Probert, Editor of "The MapInfo Professional" journal

When not writing articles for "The MapInfo Professional", Tom enjoys talking to MapInfo Professional users at conferences and events. When not working he likes to see movies with car chases, explosions and kung-fu fighting.