Question

Help with query to DBF table!

Asked by: miyahira

Hello,

We get a dbf table with field page_number. Field page_number should have continuing values like: 1,2,3,..., 100. However, constantly we get the dbf table with missing values. For example in this list: 1,2,3,6,7,8,9,10. It's missing number 4 and 5.

Is there any SQL query that we can run to know which values are missing in the DBF, knowing first value and last value of the DBF?

I'm trying to make one, but I'm stuck with that.

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Asked On
2009-10-15 at 15:05:49ID24816560
Topics

FoxPro Database

,

dBase

,

Databases Miscellaneous

Participating Experts
3
Points
500
Comments
5

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Answers

 

by: JF0Posted on 2009-10-15 at 16:16:51ID: 25585790

Do you require a SQL query only solution? This is just an example, but it will place the missing numbers in a new field called "missing" and assumes both the "numbers" field and "missing" fields are character. You can then query this "missing" field.

GO top
ilast = 0
SCAN all
   icurrent = VAL(numbers)
   IF icurrent != ilast + 1
       replace missing WITH ALLTRIM(STR(RECNO()))
       ilast = VAL(missing)
   ELSE
        ilast = icurrent
   ENDIF
ENDSCAN

 

by: pcelbaPosted on 2009-10-15 at 16:35:54ID: 25585878

The minimum missing page_number value is easy:

SELECT MIN(RECNO()) AS MinMissing ;
   FROM YourTable ;
 WHERE page_number <> RECNO()

The maximum missing page_number is more complex and requires VFP9:

SELECT MIN(page_number)-1 AS MaxMissing ;
   FROM YourTable ;
 WHERE page_number - RECNO() = (SELECT MAX(page_number-RECNO()) FROM YourTable)

In earlier VFP versions you have to calculate subquery separately.

And because the table can contain deleted records and SET DELETED can be ON the best solution is classic xBase code (suppose page_number values are unique and growing when no order is set):


LOCAL lnMinMissing, lnMaxMissing, lnExpectedPageNo
lnExpectedPageNo = 1
STORE 0 TO lnMinMissing, lnMaxMissing
 
SELECT YourTable
SCAN
  IF page_number <> lnExpectedPageNo
    IF lnMinMissing = 0
      lnMinMissing = lnExpectedPageNo
    ENDIF
    IF page_number - 1 > lnMaxMissing
      lnMaxMissing = page_number - 1
      lnExpectedPageNo = page_number
    ENDIF
  ENDIF
  lnExpectedPageNo = lnExpectedPageNo + 1
ENDSCAN
 
IF lnMinMissing = 0
  ? "No missing values"
ELSE
  ? "Minimum missing value", lnMinMissing
  ? "Maximum missing value", lnMaxMissing
ENDIF
                                              
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by: pcelbaPosted on 2009-10-15 at 16:48:55ID: 25585936

If page_number column is not ordered and eventually if it does not start at 1, you may use following code which lists all missing page numbers:

LOCAL lnExpectedPageNo
 
SELECT DISTINCT page_number ;
  FROM YourTable ;
 ORDER BY page_number ;
  INTO CURSOR cPages
 
lnExpectedPageNo = page_number
 
SCAN
  DO WHILE page_number <> lnExpectedPageNo
    ? "Missing page_number", lnExpectedPageNo
    lnExpectedPageNo = lnExpectedPageNo + 1
  ENDDO
  lnExpectedPageNo = lnExpectedPageNo + 1
ENDSCAN
                                              
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by: CaptainCyrilPosted on 2009-10-15 at 22:14:43ID: 25587170

SELECT table
CALCULATE MIN(page_number), MAX(page_number) TO nMinPage, nMaxPage
 
CREATE CURSOR allpages (page_number N(4))
FOR i = nMinPage to nMaxPage
   INSERT INTO allpages (page_number) VALUES (i)
ENDFOR
 
SELECT page_number;
FROM allpages;
WHERE page_number NOT IN (SELECT page_number FROM table);
ORDER BY page_number;
INTO CURSOR missingpages
                                              
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by: pcelbaPosted on 2009-10-15 at 22:34:30ID: 25587218

Small enhancement:

CREATE CURSOR allpages (page_number N(INT(LOG10(MAX(ABS(nMinPage), ABS(nMaxPage))))+2))

20120131-EE-VQP-002

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