DB filters

This form allows you set filters for the data base. Select database filtering from the data base display table.  There is also a Quick filtering option.


Parts to the DB filters form:
  1. Tabs to create filter
  2. Plot and accept options


Create main filter condition.  You must create at least one condition before you can filter.

  • use edit boxes at the top of the form, and then click "Add condition" button.
    • Select the DB field with the drop down box DB Field in the center of the form.  You can type in the value if you are sure you can spell correctly.  Since the length of the field names is limited, they might be abbreviated.
    • Use the drop down boxes to set the operator (=, <>, <, <=, and so on). The operators available will depend on the type of field.
    • For numerical fields, you can use the < and > operators.  You can make a complex condition, like "8< HEIGHT < 18", which the program will convert to "HEIGHT > 8 AND HEIGHT < 18" which is what the program actually needs.
    • For text fields, you can use the =  and <> operators.
    • If the field is an integer or string (and should not have too many unique values) you can:
      •  "Query field" button will find all unique values in a text field, and the range of values in a numerical field.  This avoids spelling or typing issues, and can show you have the database was populated. 
      •  "OR" button lets you select multiple values in the fields, and adds a filter that uses OR. 
  • writing directly in the memo box

The "Add condition" button moves the filter criteria to the middle box.

Add addition criteria by repeating the process.

Edit the condition in the memo box, for example:

  • Change "=" to "<>", or "<" to "<=".
  • Use "OR" joins between lines, as the default will be "AND".  Type the "OR" at the end of the line, and then use the delete key to move the next line up to become part of the single condition.

After the condition is added, the "Apply filter" button becomes active and  uses the filter on the data set.

The quick filter button accepts the criteria and immediately filters.  This is useful for single, simple filters.

Multiple conditions can be added.  Each will be on a separate line, and they will be concatenated with an "AND".  If you want an "OR", edit the filter display by adding the "OR" manually and then putting the second condition on the same line.

The "*" character acts as a wildcard; thus "M*" in a state field will find MA, MD, MO....

Filters are case sensitive or not, depending on how you set the checkbox.

The Clear button removes all filter conditions.


Create Time Filter.


Plot and accept options

  • Apply Filter button exits the form. If Redraw on close is checked, it will plot the filtered day.
  • Cancel aborts.
  • Plot takes the current filter and symbol and overlays the results on the map. If clear layer is checked, the layer will be erased before drawing.  Otherwise the filtered data will plot over the other data.
  • + Layer: add symbology to layer file.
  • Clear Layer: clears any layer symbology, and replaces it the current filtered set.  If unchecked, the new display will draw above the previous display of the layer.
  • Redraw on close: automatically redraw layer when the filter window closes.
  • Set USE on close: all records matching the filter will be set the "Y", and the rest to "NO"


For a text field with discrete values, you should select the "Query Field" button. This will give you a selection box with all the values. You many find poor quality control in the edit process of data base creation, with mis-spelled words or multiple variants for what should be the same coding.

Note in this case that "Cinder cone" and "Cinder cones", and "Complex volcano" and "Complex volcanoes" are used. You can use the wild card to find both variants, as in "Cinder cone*", or use the OR button.

Last revision 7/19/2022