Question

Two confusing examples of string matching behavior

Asked by: fuze44

Just when I think I understand!

Example 1:

I'm searching by SS#.   They're stored as Char in the table.  Regardless of the setting of SET EXACT, when my condition reads: WHERE TRIM(ssnum) = "45", the SQL Select pulls records containing no SS# as well as those starting with 45. When I remove the TRIM(), it only pulls the latter (as I want).

(I took all joins out of my SQL Select to ensure it wasn't muddling the issue.)

I don't get why "" = "45" is pulling the blank records.  I have studied the chart at http://msdn.microsoft.com/en-us/library/9z694sba(VS.80).aspx repeatedly.  My case seems to match its example of "" = "ab" which should result in a NO MATCH.


Example 2:

For reasons unimportant, I'm trying to offer the ability to enter a few numbers of the account number (which is the PK) and have all account numbers returned that begin with the criteria.  Using TRIM(TRANSFORM(user.acctnum)) = "45" I do the results I want, but it also includes the account number 4 in the list.   In this case, no combination of TRIM() and SET EXACT result in a list that doesn't include account number 4.  

Will someone enlighten me?

Thank you.

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Asked On
2009-07-03 at 17:57:07ID24543299
Topic

FoxPro Database

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Answers

 

by: tusharkanvindePosted on 2009-07-03 at 21:48:53ID: 24775744

SQL SELECT does not check the value of SET EXACT ON/OFF. Instead it checks the value of SET ANSI ON/OFF

 

by: CaptainCyrilPosted on 2009-07-03 at 23:23:00ID: 24776051

Are you sure the fields in your database all start do not start with a space?

You could also use

WHERE LEFT(SSN,2) == "45"

 

by: Olaf_DoschkePosted on 2009-07-04 at 10:07:21ID: 24777365

Whil ANSI is the setting for SQL, I can't reproduce what you're saying, that you get records without any SSN if you filter ssn='45'. Only Set Ansi Off in combination with where SSN='4' results in all SSN starting with 4, not only 4. Ansi On makes it work like expected.

If you want 'normal' behavior, SET ANSI ON, and for matching a condition "begins with 4" use LIKE '4%'

Bye, Olaf.

Create Cursor curTest (ssn C(2))
Insert into curTest values ('  ')
Insert into curTest values ('45')
Insert into curTest values ('4 ')
Set Ansi Off
select * from curTest where ssn='45'
Set Ansi On
select * from curTest where ssn='45'
Set Ansi Off
select * from curTest where ssn='4'
Set Ansi On
select * from curTest where ssn='4'
                                              
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by: jrbbldrPosted on 2009-07-04 at 16:08:52ID: 24778301

When you say..   "pulls records containing no SS# "

Are those bad record values  NULL  or   Empty?

I have seen situations where a NULL record value is returned on a query when it was not wanted, but, like Olaf has confirmed above, Blank records were not.

One way to eliminate NULL records would be to use an additional WHERE parameter (or two)

WHERE <normal criteria>;
AND NOT NULL(ssn);
AND NOT EMPTY(ssn)

Alternatively you could use the SET NULL ON/OFF environment parameter or the NVL() function.

Good Luck

 

by: Olaf_DoschkePosted on 2009-07-05 at 03:18:31ID: 24779449

jrbbldr, good point! I tested a nullable ssn and NULL would still not be in the result with ANSI ON or OFF. And as empty values is are no problem you could simply do the where clause as NVL(ssn,'') LIKE '4%'.

Bye, Olaf.

20120131-EE-VQP-002

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