Program:  Superbase
Version:  2.0
Date:     November 2, 1992
Topic:    Query-By-Form using Superbase

Summary: This technote addresses a different method of
creating queries than the usual filter dialog, Quick
Reports, or Query by Example (QBE). This method is generally
referred to as Query-By-Form. It is a simple method of
building queries providing a no training query interface for
end-users. This technote takes advantage of the extra
procedure libraries provided with Version 2.0 of Superbase
to make an easy and intuitive query interface.

Overview

What makes this technique possible is a User-defined
procedure called FilterByFile() provided with Superbase
version 2.0. The procedure uses the current file and record
to create a filter. This filter can be viewed by setting the
second parameter to 1. Shown below is a simple example of
using FilterByFile().

Example SBL code:

     OPEN FORM "test"
     LOAD "c:\sb4w\examples\procs\sblexten.sbp", NEW
     BLANK
     FORM
     ENTER
     CALL FilterByFile(0,0)
     SELECT FIRST
     FORM

How it works

OPEN FORM "test"
     Opens a form and its assorted data files.

LOAD "c:\sb4w\examples\procs\sblexten.sbp", NEW
     Loads the procedure file SBLEXTEN.SBP into memory.
     The NEW keyword specifies that it should not replace
the current program in the program editor.

BLANK
     Creates a new empty record in memory.

FORM
     Forces the screen to be refreshed with the empty
record.

ENTER
     Puts the user in the form so one can enter the query
criteria.

CALL FilterByFile(0,0)
     This is the routine in the procedure library that
actually builds the filter that is used. The first
parameter specifies if you want to exclude read-only (1 for
yes, 0 for no). The second parameter specifies if you want
the Filter dialog box to be displayed to the user after the
routine builds the query filter from the current form (1 for
yes, 0 for no).

SELECT FIRST
     Sets the file pointer to the first selected record.

FORM
     Displays the current record.

Notes on using this example:
*    On a linked form, the filter works strictly off the
     master.
*    Since this technique takes advantage of creating a
     blank entry record in memory to hold the query data,
     this method is easier to implement if your data file
     definition has no unique indexes or required fields.
     Otherwise, special handling of query entry is required.
*    Also, the user should not be allowed to save the record
     they are entering for the query by form.  This could be
     done by SET MENU OFF or by using a custom menu with the
     Save item disabled.
*    Very complex queries could be created using this
     example, so the user could trap for Query too Complex
     errors.