Database Toolbox™

Working with Preferences

Specifying Preferences

This section describes how to set VQB preferences to specify:

• How NULL data in a database is represented after you import it into the MATLAB^® workspace

• The format of data retrieved from databases

• The method of error notification

1. Click Query > Preferences. The Preferences dialog box appears.

   

2. Specify the Preferences settings as described in the following table.

   Preference	Value	Description
   Read NULL numbers as	0	If you accept the default value for this field, NULL data imported from databases into the MATLAB workspace appears as NaN. Setting this field to 0 causes NULL data imported into the MATLAB workspace to appear as 0s.
   Data return format	numeric	Select a data format based on the type of data you are importing, memory considerations, and your preferred method of working with retrieved data. Cell arrays and structures support mixed data types, but require more memory and process more slowly than numeric matrices. Select numeric if: The data you are retrieving is numeric, or You need to convert nonnumeric data to the format specified in the Read NULL numbers as field.
   Error handling	report	Set this field to store or empty to direct errors to a dialog box rather than to the MATLAB Command Window. Set this field to report to display query errors in the MATLAB Command Window.

3. Click OK.

4. Assign the query results to a workspace variable, A.

5. Click Execute to rerun the query.

   Information about the retrieved data appears in the Data area.

6. To see the results, enter A in the Command Window.

   A =
   
         125970        1400        1100         981
         212569        2400        1721        1414
         389123        1800        1200         890
         400314        3000        2400        1800
         400339        4300           0        2600
         400345        5000        3500        2800
         400455        1200         900         800
         400876        3000        2400        1500
         400999        3000        1500        1000
         888652           0         900         821
   

   NULL values appear as 0s instead of NaNs.

   For more information about Preferences, see the setdbprefs function reference page.

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Saving Preferences

Preferences apply only to the current MATLAB software session. They are not saved with queries. Default Preferences apply when you start a new session, or after you clear all variables (using, for example, the clear all command). It is a good practice to check Preferences settings before you run queries.

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Getting Started with Visual Query Builder

Displaying Query Results