How to Return the Maximum Value in a Database Field

ID: Q117218

2.00 2.50 2.50a 2.50b 2.60 | 2.50 2.50a 2.50b 2.60 3.00 | 2.50b 2.50c

MS-DOS                     | WINDOWS                    | MACINTOSH

• Microsoft Visual FoxPro for Windows, version 3.0
• Microsoft FoxPro for MS-DOS, versions 2.0, 2.5, 2.5a, 2.5b, 2.6
• Microsoft FoxPro for Windows, versions 2.5, 2.5a, 2.5b, 2.6
• Microsoft FoxPro for Macintosh, versions 2.5b, 2.5c

SUMMARY

FoxPro does not provide a function for returning the maximum value stored in a field in a database. However, FoxPro does provide the command verb CALCULATE expr list> MAX() TO memvar. Although this command is useful, you may need to call a function that will find and return the maximum value in a field for a given condition. To do this, you can use the sample code shown below, which returns the maximum value in a field in any specified table for any given condition.

NOTE: There are several ways of writing this function; this is only one example of how to write it.

MORE INFORMATION

   **************************************************************
   *                                                            *
   *  Function:     DBMAX()                                     *
   *  Parameters:                                               *
   *      fieldname   C   Required                              *
   *      workarea    N/C Optional                              *
   *      condition   C   Optional                              *
   *                                                            *
   *                                                            *
   *  Purpose: Returns the highest value of any field in the    *
   *           current or specified work area for any logical   *
   *           condition.                                       *
   *                                                            *
   *  NOTE: When you are finding the maximum of a field that is *
   *  not in the current work area, the alias must be supplied  *
   *  in the first parameter.                                   *
   **************************************************************

   PARAMETERS fieldname, workarea, condition

   **************************************************************
   * Store parameter count and current work area to memory
   * variables.
   **************************************************************

   STORE PARAMETERS() TO parms
   STORE SELECT() TO currselect

   **************************************************************
   * Store current record and total records to memory variables.
   * Initialize m.max memory variable.
   **************************************************************

   reccount = RECCOUNT(IIF(parms>1,workarea,currselect))
   currecord = RECNO(IIF(parms>1,workarea,currselect))
   m.max = 0

   **************************************************************
   * Select the correct work area if not current work area.
   **************************************************************

   IF parms > 1
      SELECT (workarea)
   ENDIF

   **************************************************************
   * Position cursor at top of file. Begin maximum loop.
   **************************************************************

   GO TOP
   SCAN FOR IIF(parms > 2,EVALUATE(condition),.T.)
   **************************************************************
   * Use a SCAN loop to move through the database and evaluate
   * the previous record with the current record and return the
   * greater value.
   **************************************************************
      SKIP -1
      STORE EVALUATE(fieldname) TO m.oldmax
      m.max = MAX(EVALUATE(fieldname),m.max,m.oldmax)
      SKIP 1
      SET MESSAGE TO ALLTRIM(STR(m.max,10,2))
   ENDSCAN

   **************************************************************
   * NOTE: The SCAN loop above could be replaced by the following
   * code:
   *
   *    CALCULATE FOR IIF(parms > 2,EVALUATE(condition),.T.)
   **************************************************************

   **************************************************************
   * Reset record pointer.
   **************************************************************

   DO CASE
      CASE currecord > reccount
         GO BOTTOM
         SKIP 1
      CASE currecord < reccount
         GO TOP
         SKIP -1
      OTHERWISE
         GO currecord
   ENDCASE

   **************************************************************
   * Select the original work area if necessary.
   **************************************************************

   IF parms > 1
      SELECT (currselect)
   ENDIF

   SET MESSAGE TO
   RETURN m.max
   ENDIF

   USE customer IN 1
   SELECT 0
   ? dbmax("customer.ytdpurch",1,"state = 'NC'")

Keywords          : kbcode FxenvMemory 
Version           : 2.00 2.50 2.50a 2.50b 2.60 | 2.5
Platform          : MACINTOSH MS-DOS WINDOWS