DOCUMENT:Q135616  24-AUG-1999  [foxpro]
TITLE   :How to Remove Records from a Table Without Using Delete/Pack
PRODUCT :Microsoft FoxPro
PROD/VER:
OPER/SYS:
KEYWORDS:

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The information in this article applies to:

 - Microsoft Visual FoxPro for Windows, version 3.0 
 - Microsoft FoxPro for MS-DOS, versions 2.0, 2.5, 2.5a, 2.6, 2.6a 
 - Microsoft FoxPro for Windows, versions 2.5, 2.5a, 2.5b, 2.6, 2.6a 
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SUMMARY
=======

Using the DELETE or PACK commands to remove records can be very time consuming.
ZAP is very fast, but removes all the records. With FoxPro's low-level file I/O,
you can quickly remove a select number of unwanted records from the end of a
table.

MORE INFORMATION
================

Step-by-Step Procedure
----------------------

1. Open a program file, name it Lowlevel.prg, and type the following function
   code:

      FUNCTION ZAPLAST
      PARAMETER lnY
      IF USED()
        lnZ=RECCOUNT()
        IF lnY<=lnZ
          lcFILENAME=DBF()
          USE
          lnHANDLE=FOPEN(lcFILENAME,2)
          IF lnHANDLE>0
            lcBYTE=FREAD(lnHANDLE,32)
            lnFLD_SIZE=ASC(SUBSTR(lcBYTE,11,1))+;
               (ASC(SUBSTR(lcBYTE,12,1))*256)
            lnFILESIZE=FSEEK(lnHANDLE,0,2)
            lnX=lnZ-lnY
            lcBYTE8=CHR(INT(lnX/(256*256*256)))
            lcBYTE7=CHR(INT(lnX/(256*256)))
            lcBYTE6=CHR(INT(lnX/256))
            lcBYTE5=CHR(MOD(lnX,256))
            lcBYTE=SUBSTR(lcBYTE,1,4)+lcBYTE5+;
               lcBYTE6+lcBYTE7+lcBYTE8+SUBSTR(lcBYTE,9)
            =FSEEK(lnHANDLE,0)
            =FWRITE(lnHANDLE,lcBYTE)
            =FCHSIZE(lnHANDLE,lnFILESIZE+(lnFLD_SIZE*lnX))
            =FCLOSE(lnHANDLE)
          ENDIF
          USE &lcFILENAME
        ENDIF
      ENDIF

2. Save and close Lowlevel.prg

3. Test the function by removing a single record from a table. For this example,
   use the Customer.dbf table - but back up the table first. Records that are
   deleted with ZAPLAST() cannot be recovered.

   a. In the Command window, type:

         SET PROCEDURE TO LOWLEVEL.PRG
         USE C:\FPW26\TUTORIAL\CUSTOMER EXCLUSIVE

   b. Take note of how many records are in the table. For this example, there
      are 500 records.

   c. In the Command window, type:

         =ZAPLAST(1)

   d. Note that there is one less record in the database. Originally there were
      500 records; now there are only 499.

4. Any number of records can be deleted. For example, to delete 27 records,
   change step 3.c. to =ZAPLAST(27)

NOTE: Only records at then end of the table can be deleted with ZAPLAST().
ZAPLAST() will not recognize index orders or Visual FoxPro triggers.

Additional query words: VFoxWin FoxWin FoxDos

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Keywords          :  
Technology        : kbVFPsearch kbAudDeveloper kbFoxproSearch kbZNotKeyword3 kbFoxPro200DOS kbFoxPro250DOS kbFoxPro250aDOS kbFoxPro260DOS kbFoxPro260aDOS kbFoxPro260 kbFoxPro250 kbFoxPro250a kbFoxPro250b kbFoxPro260a kbVFP300

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Copyright Microsoft Corporation 1999.